Practice Test - NEET MCQ

In the photoelectric effect, the work function is the minimum amount of energy (per photon) needed to eject an electron from the surface of a metal.Electrons ejected from a sodium metal surface were measured as an electric current.The minimum energy required to eject an electron from the surface is called the photoelectric work function.
This energy (work function) is a measure of how firmly a particular metal holds its electrons. The work function is important in applications involving electron emission from metals, as in photoelectric devices and cathode-ray tubes.

We know that
1/λ​=R(1/n²​₁​−1/n²₂​​)
1/λ=R(1/2²) − (1/3²​)⇒R(1/4)−(1/9​)
1/λ​=(9−4​/36)R=5R​/36⇒λ=36​/5R

The speed of revolving electron in nth state of hydrogen atom is:
v=​e²/2nhϵ₀ ​
For n=1,
v= (1.6×10⁻¹⁹)^2​/2(1)(6.6×10⁻³⁴)(8.85×10⁻¹²)
v=2.56×10^−38​/116.82×10⁻⁴⁶
 
v=0.0219×10⁸ms⁻¹
The speed of light is 3×10⁸
Hence, 
v/c​=0.0219×10^8​/3×10⁸
v/c​=1/137
 

Nucleus of hydrogen has only one proton. Hence its binding energy will be zero. The nuclear binding energy is the energy it takes to separate all the nucleons in a nucleus from each other. Since there is only the one nucleon, it's already separated from any other nucleons.

The fusion of hydrogen into helium is more likely to take place at high temperature and high pressure, like the sun.

Cl show different oxidation state as -1 to +7 due to vacant d orbital.

As oxygen is more electronegative than Cl.

Oxygen size is small hence its more electronegative and show -2 oxidation states.

2x + 7 (-2) = 0

x = +7

Autoxidation is any oxidation that occurs in presence of oxygen. The term is usually used to describe the degradation of organic compounds in air (as a source of oxygen). Autoxidation produces hydroperoxides and cyclic organic peroxides.

When zinc is placed in copper nitrate solution the intensity of the blue colour is produced and copper iron is deposited on zinc. This is a Redox reaction between zinc and an aqueous solution of copper nitrate occurring in a beaker.

Concept of Reducing Agent:
A reducing agent is a substance that loses or "donates" an electron to another substance in a redox chemical reaction. Therefore, a good reducing agent is the one that gets oxidized easily, or in other words, the one that can easily lose electrons.

Characteristics of a Good Reducing Agent: Electron Loss: A better reducing agent is the one that loses more electrons. This is because by losing electrons, the reducing agent gets oxidized and in turn reduces the other substance. This is the basic principle of a redox reaction. Reactivity: The reactivity of the metal also determines its capacity as a reducing agent. Metals that are high in the reactivity series are good reducing agents. This is because they can easily lose electrons and get oxidized. Stability: Metals that are less stable are better reducing agents because they can easily lose electrons to attain a stable state. Hence, Option A is the correct answer - a better reducing agent is the one that loses more electrons.

The flow of current in a Daniel cell or any other electrochemical cell is due to the movement of electrons from the anode to the cathode. This happens through an external circuit connecting the two electrodes.

Potential Difference: The potential difference between the two electrodes in a Daniel cell is what drives the flow of current. When zinc is oxidized at the anode, it leaves behind electrons, creating a negative charge. At the same time, the reduction of copper ions at the cathode absorbs electrons, creating a positive charge. This difference in charge creates a potential difference or voltage that causes the electrons to flow from the anode to the cathode, generating current. Therefore, option B is correct.

In conclusion, the flow of current in a Daniel cell is possible if there is a potential difference between the copper and zinc electrodes. This potential difference drives the movement of electrons from the anode to the cathode, generating current.

• Oxidation Numbers of Halogens: The halogens (Fluorine, Chlorine, Bromine, Iodine, and Astatine) are a group in the periodic table. They are known for their high electronegativity and hence, when they combine with almost all other elements, they tend to have an oxidation number of -1 as they gain one electron to achieve a stable electronic configuration.
• Exception in the case of Oxygen: However, oxygen is more electronegative than all halogens except fluorine. So, when halogens (chlorine, bromine, and iodine) combine with oxygen, they tend to lose electrons to oxygen and hence, they show positive oxidation states.
• Conclusion: Therefore, when chlorine, bromine, and iodine are combined with oxygen, they have an oxidation number of +1 or any positive number (depending on the number of oxygen atoms they are combined with). Hence, the correct answer is C: +1 or any positive number.

Preparation of Hydrogen from H₂O with Ca (Calcium)

Hydrogen can be prepared from water (H₂O) through a chemical reaction with calcium (Ca).

In this reaction, calcium acts as a reducing agent. This is because calcium has the ability to donate electrons during the reaction, which reduces the other reactant, in this case, water.

The overall chemical reaction that occurs is: Ca + 2H₂O → Ca(OH)₂ + H₂

In this reaction, calcium (Ca) reacts with water (H₂O) to form calcium hydroxide (Ca(OH)₂) and hydrogen gas (H₂).

The hydrogen gas that is produced can be collected and used for various purposes.

Thus, out of the given options, it is calcium that can act as a reducing agent to prepare hydrogen from water.

Conclusion: Therefore, the correct answer is option B: 'Ca, which acts as reducing agent'.

• Molecules of most electronegative elements, compounds having an element in the highest oxidation state and oxides of metals and nonmetals are examples of oxidising agents.
• But sodium hydride is a metallic hydride, so it is not an oxidizing agent.

Hibernation is an adaptation which has evolved in certain group of animals to conserve energy by slowing down metabolism and keeping their body temperature low in winters.

• Bats and bears are well known for hibernating. Some of the hibernating animals includes fish, frogs and turtles, snakes, bees, hedgehogs which have no way to keep warm during winter.
• Hibernation helps animal to survive when there is inadequate food supply. Before entering into hibernating state an animal stores enough fat to consume it during hibernation.

So, the correct option is 'Hibernation'.

• Ecology is the study of interaction between living organism and their environment. The basic unit of study in ecology is organism.
• An organism is a single living entity that can carry out all the functions of life, such as obtaining energy and nutrients, responding to the environment, and reproducing.

• A xerophyte is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert or an ice- or snow-covered region in the Alps or the Arctic.
• Succulent (a xerophyte) plants store water in their stems or leaves.

• This is a large regional unit characterised by a major vegetation type and associated fauna found in a specific climate zone.
• The biome includes all associated developing and modified communities occurring within the same climatic region, e.g., forest biomes, grassland and savanna biomes, desert biome, etc.
• On a global scale, all the earth’s terrestrial biomes and aquatic systems constitute the biosphere.

The Father of Ecology in India is Ramdeo Misra.

• Raja Ram Mohan Roy was a freedom fighter.
• Verghese Kurien is the Father of the White Revolution of India while MS Swaminathan is the Father of Green Revolution of India.

The place where a particular organism lives called a habitat.

• It is a place where an organism can find shelter, food, mates for reproduction and, protection from predators.
• It depends on both biological and physical factors present within it.

Homeotherms: Animals who maintain a constant internal body temperature across a wide range of environmental conditions. Most mammals and birds are homeotherms.

Decomposers breaks the complex organic matter present in dead plants and animals into simpler form that can be reused. They acts as reducer of dead and decaying matters.

Ecosystem consists of biotic component producer, consumer and decomposer. Producer fix solar energy into useable forms and decomposer breaks the complex organic matter into simpler forms but consumer do not perform specific function so non-essential.

In most of the food chain of ecosystem only 4 to 5 trophic levels are present because loss of energy at successive levels is very high. Only 10% of energy is transferred to next trophic level.

A detritus food chain begins with dead organic matter. It is made of decomposers which are heterotrophic organism fungi and bacteria.Rhizophora species is a saprophyticheterotrophs.

Food web is formed by interaction between a numbers of food chains having common members. Stability of ecosystem largely depends upon the kinds of food web exists in it for proper flow of energy.

The Red Data Book is the state document established for documenting rare and endangered species of animals, plants and fungi as well as some local sub-species that exist within the territory of the state or country. 

• IUCN is International Union for Conservation of Nature, this system is designed to determine the relative risk of extinctin
• The main purpose of the IUCN Red List or red data book is to catalogue and highlight those plants, fungi and animals that are facing a higher risk of global extinction (i.e. those listed as Critically Endangered, Endangered and Vulnerable).

Species of reptiles, amphibians and other vertebrates are becoming extinct in Haiti as deforestation has claimed more than 99 percent of the country's original wooded areas.

According to the IUCN regional red listing guidelines: 
- 12% of all the birds species
- 23% of all mammals species
- 31% of all gymnosperms species
- 32% of all amphibian species

These species face the threat of extinction in the world and have the highest percentage of endangered species, and the threats including habitat loss, fragmentation and degradation, pollution, climate change, and invasive alien species.

For greater efficiency a food chain must have three to four trophic levels. At each trophic levels loss of energy is very high so very small amount of energy is left after there trophic level.