Practice Test - NEET MCQ

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

James Chadwick set up an experiment to test his hypothesis. Chadwick put a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted the mysterious neutral rays.

A moderator is used in nuclear reactors in order to slow down the speed of neutrons.
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235 or a similar fissile nuclide.
Clearly, an obvious way to make a reactor work, and to make use of this characteristic of the 235U(n,f) cross-section, is to slow down the fast, fission neutrons. This can be accomplished, for example, when the neutrons collide with nuclei and scatter in some substance (a moderator).
 

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

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.

The reaction of metallic cobalt in a nickel sulfate solution involves a competition for the release of electrons. This means that the cobalt metal can react with the nickel ions in the solution, or the nickel can deposit on the cobalt metal.

At equilibrium, the reaction has balanced out with no net change in the concentration of the reactants and products. The fact that both Ni⁺² (aq) and Co⁺² (aq) are present at moderate concentrations at equilibrium signifies that neither forward nor reverse reactions are greatly favoured.

A: This option is incorrect because both reactants and products are present in moderate concentrations, indicating that neither is greatly favoured.

B: This statement is not correct either. Even though Co (s) and Ni⁺² (aq) are part of the reaction, the fact that Co⁺² (aq) is also present at moderate concentrations shows that they are not the only favoured species.

C: This option is also incorrect. Even though Co⁺² (aq) and Ni (s) are part of the reaction, the fact that Ni⁺² (aq) is also present at moderate concentrations shows that they are not the only favoured species.

D: This is the correct answer. When a reaction is at equilibrium, it means that the rate of the forward reaction equals the rate of the reverse reaction. Therefore, neither the reactants nor the products are greatly favoured. In other words, the concentrations of the reactants and products remain constant over time

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.

A disproportionation reaction is a particular type of redox reaction in which a single compound is transformed into two different compounds, one being reduced and the other being oxidized.

The decomposition of hydrogen peroxide to form water and oxygen is a classic example of a disproportionation reaction.

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.

Primary productivity is the rate at which solar energy is converted and stored by the producers per unit area over a time period. It involves the conversion of solar energy into organic substances by photosynthetic and chemosynthetic autotrophs.

The chemical energy of food is the main source of energy required by all living organisms. This energy is transmitted to different trophic levels along the food chain. This energy flow is based on two different laws of thermodynamics:

• First law of thermodynamics, that states that energy can neither be created nor destroyed, it can only change from one form to another.
• Second law of thermodynamics, that states that as energy is transferred more and more of it is wasted.

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 “active chemical drug reserpine” is obtained from Rauwolfia.
Reserpine is an “indole alkaloid” obtained from the roots of “Rauwolfia serpentine” and “Rauwolfia vomitoria”. It was first isolated from the dried roots of Rauwolfia in 1950. It is widely used as an antihypertensive and antipsychotic drug. It is an adrenergic blocker.

Rauwolfia serpentina:

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.