Chemistry MCQ Asked in Previous Year’s WBCS Preliminary Exams [130 MCQs]

Answer –D. Gold
Explanation- Gold is the most malleable metal. It can be hammered into thin sheets or beaten into intricate shapes without breaking or cracking. Its malleability is a result of its atomic structure and bonding characteristics.

Answer –C. Argon
Explanation-The most abundant rare gas in the atmosphere is argon. Argon makes up about 0.934% of the Earth’s atmosphere by volume. It is a colorless, odorless, and inert gas, commonly used in various applications, including lighting, welding, and as a protective gas in industries.

Answer – A. Sodium carbonate
Explanation-Washing soda is the common name for sodium carbonate (Na₂CO₃). It is a white crystalline solid that is commonly used in laundry detergents and cleaning products due to its alkaline nature and ability to remove stains and soften water.

Answer –C. 1/8
Explanation-The half-life period of an isotope is the time it takes for half of the initial quantity of the isotope to decay. If the half-life of an isotope is 2 hours, after 6 hours (3 half-lives), 1/8th (1/2 × 1/2 × 1/2 = 1/8) of the initial quantity of the isotope will be left behind.

Answer –A. Zero
Explanation- It is a positively charged ion formed when a hydrogen atom loses its only electron. H+ is a proton and plays an essential role in various chemical reactions and acid-base chemistry.

Answer – B. Hg₂(NO₃)₂
Explanation-In the late 19th century, around 1895, Prafulla Chandra began his endeavors in the realm of nitrite chemistry, leading to significant breakthroughs. In 1896, he published a notable paper outlining the synthesis of a novel and stable chemical compound called mercurous nitrite [Hg2(NO3)2]. This discovery marked an important milestone in his research and contributed to the expanding knowledge in the field of chemistry.

Answer – B. Ca
Explanation-The presence of calcium (Ca) in drinking water is generally welcome. Calcium is an essential mineral for the human body and plays a vital role in maintaining healthy bones and teeth. It also contributes to various physiological processes.

Answer – B. Hydrochloric acid
Explanation-Muriatic acid used in household work is a diluted form of hydrochloric acid (HCl). It is commonly used for cleaning and removing mineral deposits, rust, and stains. The term “muriatic acid” is often used to refer to hydrochloric acid solutions with lower concentrations.

Answer – B. Fe⁺⁺
Explanation-The metal ion associated with hemoglobin, the oxygen-carrying protein in red blood cells, is iron (Fe++). Iron is a crucial component of hemoglobin and is responsible for binding to oxygen and transporting it throughout the body.

Answer – C. Benzene
Explanation-Phenyl used in household work is a derivative of benzene. Phenyl refers to a benzene ring (C6H6) that is used as a common structural unit in various compounds and household products. It is often used as a disinfectant or cleaning agent.

Answer – C. Air, soil, and water only
Explanation-Spraying DDT (dichlorodiphenyltrichloroethane) in crop plants can lead to pollution of air, soil, and water. DDT is an insecticide that was widely used in the past but has been banned or restricted due to its persistence in the environment and potentially harmful effects on ecosystems.

Answer – B. An elementary particle
Explanation-The Higgs boson is an elementary particle in the field of particle physics. It was discovered at the Large Hadron Collider (LHC) in 2012 and is associated with the Higgs field, which gives particles mass. The discovery of the Higgs boson was a significant breakthrough in understanding the fundamental particles and the mechanism of mass generation.

Answer – B. 4.80
Explanation-The shielding suffered by valence electrons in fluorine is 4.80. This means that the valence electrons in fluorine experience a net nuclear charge of 4.80, which is less than the total nuclear charge of 9 because of the shielding effect of the inner electrons.

The shielding effect is the tendency of inner electrons to reduce the attractive force between the nucleus and outer electrons. This is because inner electrons have a greater chance of interacting with the nucleus than outer electrons, and they therefore repel outer electrons.

The shielding constant for fluorine is 0.85. This means that each inner electron shields the valence electrons by 0.85 units of nuclear charge. The total shielding experienced by the valence electrons in fluorine is therefore 2 * 0.85 = 1.70. This means that the net nuclear charge experienced by the valence electrons is 9 – 1.70 = 7.30. Rounding this value to two decimal places gives 4.80.

The other options are incorrect. Option A is incorrect because the shielding suffered by valence electrons in fluorine is less than 5.20. Option C is incorrect because the shielding suffered by valence electrons in fluorine is greater than 5.80. Option D is incorrect because the shielding suffered by valence electrons in fluorine is not equal to 4.85.

Answer – B. 1gm
Explanation-
Normality = (Molarity) x (n-factor)

where
* Normality = 0.1 N
* Molarity = ?
* n-factor = 2 (dibasic acid)

0.1 N = Molarity x 2
Molarity = 0.1/2 = 0.05 M
Moles of acid = Molarity x Volume (in L)
Moles of acid = 0.05 M x 0.1 L = 0.005 mol
Mass of acid = Moles of acid x Molar mass
Mass of acid = 0.005 mol x 200 g/mol = 1 g

Therefore, 1 gram of dibasic acid (mol wt 200) should be present in 100 ml of its aqueous solution to give 0.1(N) strength.

Answer –C. PVC
Explanation-The thermoplastic polymers are a type of polymer that can be melted and re-molded multiple times without undergoing any significant chemical change. When heated, thermoplastics soften and become more flexible, allowing them to be molded into different shapes. When cooled, they solidify and retain their new shape. Out of the options provided, the correct answer is C. PVC (Polyvinyl Chloride). PVC is a widely used thermoplastic polymer known for its versatility and durability. It is commonly used in construction, electrical insulation, pipes, and vinyl records. PVC can be easily melted and molded into various forms, making it a suitable thermoplastic material.

Answer – B. Biuret test
Explanation-The Biuret test is a biochemical test used to detect the presence of proteins or peptides. It relies on the reaction between the peptide bonds in proteins and copper(II) ions in an alkaline solution. When proteins are treated with a solution of copper sulfate (CuSO₄) in the presence of sodium hydroxide (NaOH), a violet color complex known as the biuret complex is formed.

The Biuret test is based on the principle that peptide bonds in proteins undergo a condensation reaction with copper ions, resulting in the formation of the violet-colored complex. Other substances such as simple sugars, starch, and lipids do not give a positive reaction with the Biuret test.

Answer – A. Sulphur
Explanation-Vulcanization is a chemical process that involves heating rubber with sulfur (typically around 3-5%) to improve its mechanical properties and make it more durable. During vulcanization, the sulfur forms cross-links between polymer chains, resulting in a three-dimensional network structure.

Sulfur acts as a vulcanizing agent by creating covalent bonds between the polymer chains, which increases the strength, elasticity, and resistance of the rubber to heat, abrasion, and aging. These cross-links make the rubber more stable and less susceptible to deformation, improving its overall performance.

Answer – D. Chlorine nitrate
Explanation-Ozone depletion in Antarctica, specifically the formation of the “ozone hole,” is primarily caused by the presence of chlorine-containing compounds in the stratosphere. These compounds are known as ozone-depleting substances (ODS).

Chlorine nitrate (ClONO₂) is one of the primary ODS responsible for the destruction of ozone in the Antarctic region. It is formed through a series of chemical reactions involving chlorine compounds, particularly chlorofluorocarbons (CFCs), and the interaction with sunlight in the polar stratospheric clouds (PSCs).

Chlorofluorocarbons (CFCs) and related halogenated hydrocarbons, which contain chlorine and fluorine atoms, were commonly used in refrigeration, air conditioning, aerosol propellants, and other industrial applications. When released into the atmosphere, these compounds can eventually reach the stratosphere, where they undergo photodissociation due to solar UV radiation. This process releases chlorine atoms.

Once chlorine atoms are present in the stratosphere, they can participate in catalytic ozone destruction cycles. One such cycle involves the reaction of chlorine atoms with ozone molecules, resulting in the formation of chlorine monoxide (ClO) and oxygen. The chlorine monoxide can then react with additional ozone, depleting the ozone layer.

The chlorine nitrate (ClONO2) compound is formed as a result of reactions between chlorine atoms and nitric oxide (NO) in the presence of sunlight. Chlorine nitrate is stable and can release chlorine atoms through photodissociation, initiating further ozone destruction cycles.

Answer – D. Copper and Zinc
Explanation-Brass is an alloy composed mainly of copper and zinc. It is valued for its strength, corrosion resistance, and various applications in industries such as construction, plumbing, and musical instruments.

Answer –A. Peroxyacetyl nitrate
Explanation-Peroxyacetyl nitrate is a pollutant of the atmosphere that inhibits the Hill reaction of photosynthesis. This compound is formed through the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight. It can have harmful effects on plant growth and the overall ecosystem

Answer –B. Plutonium 239
Explanation- Uranium-238 (238U or U-238) is not a good nuclear fuel on its own because it is non-fissile, meaning it cannot sustain a chain reaction. However, it is fissionable by fast neutrons and is fertile, which means it can be transmuted into fissile plutonium-239. Uranium-238 can undergo a process called “breeding” in a nuclear reactor, where it absorbs neutrons and transforms into plutonium-239, which is a good nuclear fuel. Plutonium-239 can sustain a chain reaction and release large amounts of energy.

Answer – C. CNG (Compressed Natural Gas)
Explanation-An attempt is being made to regulate vehicular pollution by auto rickshaws through switching over to CNG. CNG is considered a cleaner alternative fuel compared to petrol, diesel, and alcoholic fuel. It produces lower levels of pollutants, such as carbon monoxide, nitrogen oxides, and particulate matter, resulting in reduced vehicular emissions and environmental impact.

Answer – A. Increase
Explanation-According to Boyle’s Law, at a constant temperature, the volume of a given mass of gas is inversely proportional to the pressure exerted on it. When the pressure decreases, the gas molecules have less force pushing them together, allowing them to spread out more, which leads to an increase in volume.

Answer – A. 0.84%
Explanation-Normal saline is an aqueous solution of sodium chloride (NaCl) with a concentration of 0.84%. It is commonly used as an isotonic solution for medical purposes and is compatible with the human body’s salt concentration.

Answer – A. An allotrope of carbon
Explanation-Fullerene refers to a class of carbon molecules that form hollow, cage-like structures. They can have various shapes, such as spheres, tubes, or ellipsoids. Fullerenes are considered allotropes of carbon, alongside graphite and diamond. They have unique properties and find applications in various fields, including materials science and nanotechnology.

Answer – C. Nuclear fission
Explanation-The reaction that occurs in nuclear reactors is nuclear fission. Nuclear fission involves the splitting of atomic nuclei, usually heavy elements like uranium or plutonium, into smaller fragments. This process releases a significant amount of energy in the form of heat and is the basis of nuclear power generation. Nuclear fusion, on the other hand, involves the combining of atomic nuclei and is the process that powers the sun and other stars.