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All questions of Chemistry for BPSC (Bihar) Exam

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H2O is liquid and H2S is a gas because
  • a)
    oxygen forms stronger hydrogen level than sulphur.
  • b)
    oxygen is less electronegative than sulphur.
  • c)
    atomic radius of oxygen is less than that of sulphur.
  • d)
    atomic radius of oxygen is greater than that of sulphur.
Correct answer is option 'A'. Can you explain this answer?

Rahul Rathore answered
In h2o there is hydrogen bonding because oxygen has a high electronegativity(only second to flourine). so, the hydrogen atoms from other molecules of water forms a hydrogen bonds with oxygen resulting in intermolecular hydrogen bonding. ... therefore at room temperature h2o is aliquid and h2s is a gas.

Which of the following pairs is/are correctly matched?
1. Isotopes : Atoms with same atomic number but different atomic mass.
2. Isobars : Atoms with same number of neutrons but different atomic number.
3. Isotones : Atoms with same mass number but different atomic number.

Q. Select the correct answer using the codes given below :
  • a)
    1, 2 and 3
  • b)
    1 only
  • c)
    1 and 2 only
  • d)
    2 only
Correct answer is option 'B'. Can you explain this answer?

Aarya Choudhary answered
Isotopes are variants of a particular chemical element: while all isotopes of a given element share the same number of protons and electrons, each isotope differs from the others in its number of neutrons. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively

Enriched uranium is
  • a)
    Uranium rods kept under special shield
  • b)
    Natural uranium in which the component of radioactive isotope U235 is artificial increased
  • c)
    Natural uranium mixed with thorium
  • d)
    Uranium rods coated with chromium
Correct answer is option 'B'. Can you explain this answer?

Palak Nambiar answered
Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Enriched uranium is a critical component for both civil nuclear power generation and military nuclear weapons. The International Atomic Energy Agency attempts to monitor and control enriched uranium supplies and processes in its efforts to ensure nuclear power generation safety and curb nuclear weapons proliferation.

Consider the following statements:
Nitrogen is an essential constituent of
1. soils
2. animals
3. plants

Q. Which of the statements given above is/are correct ?
  • a)
    3 only
  • b)
    1 and 3 only
  • c)
    1, 2 and 3
  • d)
    1 and 2 only
Correct answer is option 'C'. Can you explain this answer?

Aarav Saini answered
Understanding the Importance of Nitrogen
Nitrogen is a crucial element that plays a significant role in the ecosystem. The statements regarding its presence in soils, animals, and plants highlight its essential nature. Let's break down each statement to understand why the correct answer is option 'C'.
1. Nitrogen in Soils
- Nitrogen is a vital nutrient found in soils, primarily in the form of organic matter and various nitrogenous compounds.
- It is a key component for the growth of crops, as it contributes to soil fertility and health.
2. Nitrogen in Animals
- Animals require nitrogen for the synthesis of amino acids, which are the building blocks of proteins and essential for various bodily functions.
- Nitrogen is present in the form of proteins and nucleic acids in animals, making it an essential constituent.
3. Nitrogen in Plants
- Plants absorb nitrogen from the soil in the form of nitrates and ammonium, which are critical for their growth and development.
- Nitrogen is a key element in chlorophyll, the molecule responsible for photosynthesis, thus influencing plant health and productivity.
Conclusion
Given that nitrogen is indeed an essential constituent of soils, animals, and plants, all three statements are correct. Therefore, the correct answer is:
c) 1, 2 and 3
This highlights the interconnectedness of nitrogen in various forms of life and its importance in maintaining ecological balance.

Which one of the following pairs is correctly matched?
  • a)
    Silver iodide — Horn silver
  • b)
    Silver chloride — Artificial rain
  • c)
    Zinc phosphide — Rat poison
  • d)
    Zinc sulphide — Philosopher’s wool
Correct answer is option 'C'. Can you explain this answer?

Kunal Roy answered
Cerargyrite, also called Horn Silver, gray, very heavy halide mineral composed of silver chloride (AgCl); it is an ore of silver. Tiny particles of silver iodide are sprayed on a cloud from an aeroplane. The particles attract water drops from the cloud. When they form a drop that is large enough, it starts raining. Zinc phosphide is an inorganic compound that is used in pesticide products as a rodenticide.. Zinc oxide is also known as philosopher's wool.

The order of appearance of the following with increasing temperature during the refining of crude oil is __________
  • a)
    Kerosene, gasoline, diesel
  • b)
    Diesel, gasoline, kerosene
  • c)
    Gasoline, kerosene, diesel
  • d)
    Gasoline, diesel, kerosene
Correct answer is option 'C'. Can you explain this answer?

Nilotpal Desai answered
Order of Appearance of Products during the Refining of Crude Oil

Introduction:
During the refining of crude oil, various products are obtained by separating the different components based on their boiling points. The order of appearance of these products depends on the temperature at which they boil. In this question, we are given the options and we need to determine the correct order of appearance of the products with increasing temperature.

Explanation:

Option a) Kerosene, gasoline, diesel:
- Kerosene has a higher boiling point than gasoline and diesel, so it should appear later in the refining process.
- Gasoline has a lower boiling point than kerosene but a higher boiling point than diesel, so it should appear in between kerosene and diesel.
- Diesel has a lower boiling point than both kerosene and gasoline, so it should appear first in the refining process.
- Therefore, option a) is not the correct answer.

Option b) Diesel, gasoline, kerosene:
- Diesel has a lower boiling point than both gasoline and kerosene, so it should appear first in the refining process.
- Gasoline has a higher boiling point than diesel but a lower boiling point than kerosene, so it should appear in between diesel and kerosene.
- Kerosene has a higher boiling point than both diesel and gasoline, so it should appear last in the refining process.
- Therefore, option b) is not the correct answer.

Option c) Gasoline, kerosene, diesel:
- Gasoline has a lower boiling point than both kerosene and diesel, so it should appear first in the refining process.
- Kerosene has a higher boiling point than gasoline but a lower boiling point than diesel, so it should appear in between gasoline and diesel.
- Diesel has a higher boiling point than both gasoline and kerosene, so it should appear last in the refining process.
- Therefore, option c) is the correct answer.

Option d) Gasoline, diesel, kerosene:
- Gasoline has a lower boiling point than both diesel and kerosene, so it should appear first in the refining process.
- Diesel has a higher boiling point than gasoline but a lower boiling point than kerosene, so it should appear in between gasoline and kerosene.
- Kerosene has a higher boiling point than both gasoline and diesel, so it should appear last in the refining process.
- Therefore, option d) is not the correct answer.

Conclusion:
The correct order of appearance of the products with increasing temperature during the refining of crude oil is gasoline, kerosene, diesel. This means that gasoline appears first, followed by kerosene, and finally diesel.

Living in the atmosphere of CO is dangerous because it
  • a)
    Reduces organic matter of tissues
  • b)
    Dries up the blood
  • c)
    Combined with O2 present inside to form CO2
  • d)
    Combines with haemoglobin and makes it incapable of absorbing oxygen
Correct answer is option 'D'. Can you explain this answer?

Devanshi Chavan answered
When CO is not ventilated it binds to haemoglobin, which is the principal oxygencarrying compound in blood; this produces a compound known as carboxyhaemoglobin. The traditional belief is that carbon monoxide toxicity arises from the formation of carboxyhaemoglobin, which decreases the oxygen-carrying capacity of the blood and inhibits the transport, delivery, and utilization of oxygen by the body.

Consider the following statements and select the correct code.
Assertion (A): A chemical reaction becomes faster at higher temperature.
Reason (R): At higher temperature, molecular motion becomes more rapid.
  • a)
    Both A and R are true and R is the correct explanation of A.
  • b)
    Both A and R are true, but R is not correct explanation of A.
  • c)
    A is true, but R is false.
  • d)
    A is false, but R is true.
Correct answer is option 'A'. Can you explain this answer?

Avi Sengupta answered
The rates of most reactions increase with a rise in temperature. Raising the temperature increases the fraction of molecules having very high kinetic energies. These are the ones most likely to react when they collide. The higher the temperature, the larger the fraction of molecules that can provide the activation energy needed for reaction.

Match List–I with List–II and select the correct answer using the codes given below :
  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'A'. Can you explain this answer?

Dipika Gupta answered
These compounds are used in the manufacture of the following products. Cellulose nitrate- Gun powder, Potassium Sulphate- Fertiliser, Potassium salts of fatty acids- Soft soap, Calcium oxide- Glass.

What is “ Kiss of death” ?
  • a)
    A flower whose smell was the basis of a discovery on smell that led to award of 2004 Nobel Prize in Medicine.
  • b)
    A chemical whose discovery ultimately won the scientists the 2004 Nobel Prize in Chemistry.
  • c)
    A good wine flavour working on which scientist won the 2004 Nobel Prize in Chemistry.
  • d)
    A network in brain associated with smell whose discovery led the scientists win the 2004 Nobel Prize in Physiology and Medicine.
Correct answer is option 'B'. Can you explain this answer?

Rithika Basak answered
Aaron Ciechanover, Avram Hershko and Irwin Rose have been awarded the Nobel Prize in Chemistry 2004 for “...helping to understand how the human body gives the 'kiss of death' to rogue proteins to defend itself from diseases like cancer” (Reuters, 6 October 2004). These scientists—the former two from Israel, the latter from the US — discovered ubiquitin-mediated protein degradation. Knowledge of ubiquitin-mediated protein degradation offers an opportunity to develop drugs against cervical cancer, cystic fibrosis and other diseases.

Which one among the following statements regarding the properties of mixtures and compounds is not correct?
  • a)
    A mixture shows the properties of its constituents but the properties of a compound are entirely different from its constituents
  • b)
    A mixture may be homogeneous or heterogeneous but a compound is a homogeneous substance
  • c)
    The constituents of a mixture can be separated by physical methods but those of a compound cannot be separated by physical methods
  • d)
    Energy is either absorbed or evolved during the preparation of a mixture but not in the preparation of a compound
Correct answer is option 'D'. Can you explain this answer?

Priya Mukherjee answered
Understanding Mixtures and Compounds
When differentiating between mixtures and compounds, it's essential to grasp their distinct properties. The statement in option 'D' claims that energy is absorbed or evolved during the preparation of a mixture but not in the preparation of a compound. This assertion is incorrect.
Energy Changes in Compounds
- Compounds are formed through chemical reactions, which typically involve energy changes.
- During these reactions, energy can be absorbed (endothermic) or released (exothermic).
- For example, the formation of water from hydrogen and oxygen releases energy, demonstrating that energy changes are indeed involved in compound formation.
Properties of Mixtures vs. Compounds
- Mixtures:
- Exhibit the properties of their individual components.
- Can be separated by physical methods (e.g., filtration, distillation).
- Can be homogeneous (uniform composition) or heterogeneous (distinct layers).
- Compounds:
- Have distinct properties that differ significantly from their constituent elements.
- Are homogeneous in nature.
- Require chemical methods for separation, such as electrolysis.
Conclusion
In conclusion, the incorrect statement is option 'D' because compounds do involve energy changes during their formation, contrary to what the statement suggests. Understanding these fundamental differences is crucial for grasping basic chemistry concepts.

Biogas mainly consists of
  • a)
    Carbon dioxide and hydrogen
  • b)
    Hydrogen and methane
  • c)
    Carbon dioxide and methane
  • d)
    Hydrogen and oxygen
Correct answer is option 'C'. Can you explain this answer?

Krithika Saha answered
Biogas is a type of renewable energy that is produced through the anaerobic digestion of organic waste materials, such as agricultural waste, sewage sludge, and food waste. It is a mixture of gases that primarily consists of carbon dioxide and methane.

The correct answer is option 'C', which states that biogas mainly consists of carbon dioxide and methane. This answer is correct because carbon dioxide and methane are the two primary components of biogas. Let's explore this answer in detail:

Components of biogas:
- Carbon dioxide (CO2): This is a colorless and odorless gas that is produced during the anaerobic decomposition of organic matter. It is a greenhouse gas that contributes to climate change.
- Methane (CH4): This is a flammable and odorless gas that is the main component of natural gas. It is produced by the anaerobic bacteria that break down organic matter in the absence of oxygen.
- Trace gases: In addition to carbon dioxide and methane, biogas may also contain small amounts of other gases such as hydrogen sulfide (H2S), ammonia (NH3), and water vapor (H2O).

Formation of biogas:
Biogas is formed through a natural biological process called anaerobic digestion. During this process, organic waste materials are broken down by bacteria in an oxygen-free environment. The bacteria convert the organic matter into biogas through a series of biochemical reactions.

Importance of carbon dioxide and methane in biogas:
- Carbon dioxide: While carbon dioxide is a greenhouse gas and contributes to climate change, the carbon dioxide produced from biogas is considered carbon-neutral. This is because the carbon dioxide released during the combustion of biogas is offset by the carbon dioxide absorbed by the plants during their growth. Therefore, biogas is considered a renewable energy source.
- Methane: Methane is a potent greenhouse gas that has a much higher global warming potential than carbon dioxide. However, capturing and utilizing methane from biogas can help reduce its impact on climate change. By using biogas as a fuel, methane emissions are significantly reduced compared to when the organic waste materials are left to decompose naturally.

In conclusion, biogas mainly consists of carbon dioxide and methane. While carbon dioxide is a byproduct of the anaerobic digestion process, methane is the main component and has the potential to be used as a renewable energy source.

Which of the following statements about diamond are correct?
1. It is used as a gem in jewellery because of its ability to reflect light.
2. It is good conductor of electricity.
3. It is used for cutting glass, marble stones and other hard materials.
4. It is used for drilling of rocks.
Q. Select the correct answer using the codes given below :
  • a)
    1, 3 and 4
  • b)
    2, 3 and 4
  • c)
    1, 2 and 3
  • d)
    2 and 4
Correct answer is option 'A'. Can you explain this answer?

Pragati Banerjee answered
Statement 1: Diamond is used as a gem in jewelry because of its ability to reflect light.
Statement 2: Diamond is a good conductor of electricity.
Statement 3: Diamond is used for cutting glass, marble stones, and other hard materials.
Statement 4: Diamond is used for drilling rocks.

Explanation:

Statement 1: It is used as a gem in jewelry because of its ability to reflect light.
This statement is correct. Diamond is known for its brilliance and ability to reflect light. It has a high refractive index, which means it can bend and reflect light in a way that makes it sparkle and shine. This property makes it highly desirable for use in jewelry.

Statement 2: Diamond is a good conductor of electricity.
This statement is incorrect. Diamond is actually a poor conductor of electricity. Unlike metals, which have a high number of free electrons that can carry an electric current, diamond is made up of carbon atoms arranged in a crystal lattice structure, which does not allow the easy movement of electrons. However, diamond can conduct heat very well due to its high thermal conductivity.

Statement 3: Diamond is used for cutting glass, marble stones, and other hard materials.
This statement is correct. Diamond is the hardest known natural material, scoring a 10 on the Mohs scale of mineral hardness. This hardness makes it ideal for cutting and grinding other hard materials, including glass, marble stones, and various industrial applications.

Statement 4: Diamond is used for drilling rocks.
This statement is correct. Diamond drill bits are commonly used in the mining and construction industries for drilling rocks and other hard materials. The hardness of diamond allows it to effectively cut through tough materials, making it an essential tool for drilling and exploration purposes.

In conclusion, statements 1, 3, and 4 are correct, while statement 2 is incorrect.

Hydrofluoric acid is not kept in glass bottles because it reacts with
  • a)
    visible light
  • b)
    sodium oxide of glass
  • c)
    aluminium oxide of glass
  • d)
    silicon dioxide of glass
Correct answer is option 'D'. Can you explain this answer?

Aashna Nambiar answered
Hydrofluoric acid is one of the most dangerous acids known. It needs to be treated differently then even strong acids like sulphuric and hydrochloric. HF reacts with many materials, therefore, avoid contact with glass, concrete, metals, water, other acids, oxidizers, reducers, alkalis, combustibles, organics and ceramics.

Match List-I with List-II and select the correct answer from the codes given below:

  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'D'. Can you explain this answer?

Advait Chawla answered
Morphine is an analgesic drug that is used to relieve severe pain. It was first isolated in 1804 by Friedrich Serturner, which is generally believed to be the first ever isolation of a natural plant alkaloid in history. Boric acid, also called orthoboric acid, is a weak acid of boron often used as an antiseptic or insecticide. Nickel silver, also known as German silver, is a copper alloy with nickel and often zinc. The usual formulation is 60% copper, 20% nickel and 20% zinc. Sodium is an extremely reactive metal and a powerful reducing agent. When exposed to air, it very quickly oxidizes. It also reacts violently to water. We store sodium under kerosene because kerosene is already highly reduced and won't react with sodium metal.

Match List-I with List-II
  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'D'. Can you explain this answer?

Sagar Chakraborty answered
The “plum pudding model” was put forward by J.J. Thomson in 1904. In this model, the atom is made up of negative electrons that float in a “soup” of positive charge, much like plums in a pudding or raisins in a fruit cake. In 1906, Thomson was awarded the Nobel Prize for his work in this field. Louise de Broglie suggested that electron exhibits a dual nature. Broglie also got Physics Noble Prize for his theory. In 1913, Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. Ernest Rutherford published his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.

The inexhaustible source of energy of the stars is due to
  • a)
    conversion of hydrogen to helium
  • b)
    conversion of helium to hydrogen
  • c)
    decay of radioactive elements
  • d)
    excess of oxygen that helps burning and release of energy
Correct answer is option 'A'. Can you explain this answer?

Raksha Khanna answered
The energy released from the collapse of the gas into a star causes the centre of the star to become extremely hot. When the core is hot enough, nuclear fusion commences. Fusion is the process where two hydrogen atoms combine to form a helium atom, releasing energy. The fusion reaction is a very efficient process, releasing a huge amount of energy. This is because a single helium atom contains less mass than two hydrogen atoms. The excess mass is released as energy.

Helium is preferred to hydrogen in air balloons because it
  • a)
    is cheaper
  • b)
    is less dense
  • c)
    has greater lifting power
  • d)
    does not form an explosive mixture with air
Correct answer is option 'D'. Can you explain this answer?

Anshul Ghosh answered
Hydrogen combines with oxygen with explosive force in the presence of a spark.Helium is an inert gas that will not burn or explode, so is much safer to use in balloons instead of hydrogen.

Q.Which of the following substances is/are ozone depleting?
1. Chlorofluorocarbons
2. Halons
3. Carbon tetrachloride
  • a)
    1 only
  • b)
    1 and 2 only
  • c)
    2 and 3 only
  • d)
    1, 2 and 3
Correct answer is option 'D'. Can you explain this answer?

Sagar Chakraborty answered
All the three substances are responsible for ozone layer depletion in different ways. Which are: CFC—mostly used in refrigeration, air conditioning and heat pump systems. Halons—used historically as fire suppression agents and fire fighting, but now only allowed in very limited situations. Carbon tetrachloride (tetrachloromethane)—limited solvent used in laboratories and chemical and pharmaceutical industries.

Match List-I with List-II and select the correct answer given below:
  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'A'. Can you explain this answer?

Avi Sengupta answered
The electron was discovered in 1896, by the British physicist J. J. Thomson, using cathode rays while doing discharge tube experiments. In 1886, Eugen Goldstein discovered the existence of a new type of rays in discharge tube and named as anode rays or canal rays. Canal or anode rays travel in straight line and are deflected by electric field towards cathode which proves that they are composed of positively charged particles. These lightest positively charged particles were named and characterised as protons by Ernest Rutherford in 1919 who purposed Rutherford model for atom to explain the atomic structure. Anti-electron or in other words the positron was discovered in 1932 by Anderson, a physicists and he found that the bombardment of boron with an alpha particle resulted in the emission of this particle. In 1932, James Chadwick, an English physicist who had worked with Rutherford, detected neutrons.

Match List-I with List-II and select the correct answer from the codes given below:

  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'A'. Can you explain this answer?

Shreya Desai answered
Manganese is essential to iron and steel production. At present, steel making accounts 85 to 90% of the total demand, most of the total demand. Manganese is a key component of low-cost stainless steel formulations and certain widely used aluminium alloys. Limestone can be used in constructing buildings. It can be used for making cement and mortar. Limestone is used to make glass and even used to make roads. Bauxite is the mineral ore of aluminium which is used in the manufacture of cans, airplanes, sporting and electronic equipment and home appliances. The Wright Brother's first airplane to fly in 1903 only was able to get off the ground because they modified its engine with aluminium in order to reduce its weight. Without the ability of the strong aluminium, alloys to withstand the huge pressures and stresses involved, high altitude flying would not be conceivable. In fact, aluminium comprises about 80% of an aircraft’s unladen weight. The element copper is used extensively as an electrical conductor, for the making of electrical wire.

Hydrogen bomb is based on the principle of
  • a)
    controlled fusion reaction
  • b)
    uncontrolled fusion reaction
  • c)
    controlled fission reaction
  • d)
    uncontrolled fission reaction
Correct answer is option 'B'. Can you explain this answer?

Rithika Menon answered
Thermonuclear fusion, or hydrogen bombs explode with enormous power using uncontrolled self-sustaining chain fusion reactions. Deuterium and tritium, under extremely high temperatures, form helium providing the energy. D + T → 4He + n In principle, a mixture of D, T and 6Li heated to very high temperature and confined to a high density will start a chain fusion reaction, liberating an enormous amount of energy.

Match List-I with List-II and select the correct answer from the codes given below


  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'A'. Can you explain this answer?

Meghana Shah answered
Quarks have fractional electric charge values– either 1/2 or 2/3 times the elementary charge. The positron has an electric charge of +1e, a spin of 1/2, and has the same mass as an electron. A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with halfinteger spin. All evidence suggest that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.

Match List-I with List-II and select the correct answer from the codes given below:
 
  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'B'. Can you explain this answer?

Anirudh Joshi answered
As a gemstone used in jewellery, silicon carbide is called "synthetic moissanite" or just "moissanite". Moissanite is similar to diamond in several important respects it is transparent and hard . Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its thermal conductivity is close to that of diamond, more than any other diamond substitute. The properties of carbon fibres, such as high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion, make them very popular in aerospace, civil engineering, military, and motor sports. Dichlorodifluoromethane (R-12) is a colourless gas, and usually sold under the brand nameFreon-12, is a chlorofluorocarbon halo-methane (CFC), used as a refrigerant and aerosol spray propellant. In photosynthesis, solar energy is converted to chemical energy. The chemical energy is stored in the form of glucose (sugar). Carbon dioxide, water, and sunlight are used to produce glucose, oxygen, and water.

What happened when a hard boiled egg after shelling is immersed in saturated brine?
  • a)
    It shrinks
  • b)
    It grows in size
  • c)
    Its size remains unchanged
  • d)
    it initially grows in size and then shrinks.
Correct answer is option 'C'. Can you explain this answer?

Nidhi Pillai answered
When hard boiled egg after shelling is immersed in saturated brine, its size remains same. Due to coagulation of inner liquid there is no flow of solvent molecules across the membrane.

Match List-I with List-II and select the correct answer from the codes given below:
  • a)
    A
  • b)
    B
  • c)
    C
  • d)
    D
Correct answer is option 'A'. Can you explain this answer?

Vaishnavi Choudhary answered
Bleaching powder or calcium hypochlorite is a chemical compound with formula Ca(ClO)2. The chemical formula for marble is CaCO3. It is calcium carbonate. Marble is used in various applications, including home design. Gypsum is a very soft sulphate mineral composed of calcium sulphate dihydrate, with the chemical formula CaSO4 · 2H2O. It can be used as a fertilizer, is the main constituent in many forms of plaster and is widely mined.

In cold weather, aquatic animals survive even when water to the top layer of the lake freezes into ice because
  • a)
    they can breathe in ice
  • b)
    they have enough of accumulated oxygen inside them
  • c)
    their body structure is such that they can survive without oxygen.
  • d)
    water has highest density of 4°C so underneath the top layer of ice there is layer of water
Correct answer is option 'D'. Can you explain this answer?

Aravind Chatterjee answered
In cold countries, when the temperature of fresh water reaches 4°C, the layers of water near the top in contact with cold air continue to lose heat energy and their temperature falls below 4°C. On cooling below 4°C, these layers do not sink but may rise up as fresh water has a maximum density at 4°C. Due to this, the layer of water at 4°C remains at the bottom and above this layers of water 3°C, 2°C, 1°C and 0°C are formed. Because ice is a poor conductor of heat, it does not absorb heat energy from the water beneath the layer of ice which prevents the water freezing. Thus, aquatic creatures survive in such places.

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