All Free Biology MCQs with Answers

• A. Sodium Chloride
• B. Sodium Carbonate
• C. Limestone
• D. Ammonia gas

Explanation: Sodium carbonate is the product of the Solvay process so it can definitely not be the raw material required for this process.

• A. Precursor of making Teflon
• B. Precursor of making refrigerants
• C. Anaesthetic
• D. Embalming chemicals

Explanation: Chloroform is commonly used to prepare Teflon and refrigerants. It has also been used as an anesthetic in history. Chloroform cannot be an embalming chemical but formaldehyde can.

• A. Oxidising smog
• B. Neutral smog
• C. Basic smog
• D. Reducing smog

Explanation: Smog is a combination of smoke and fog. There are two types of smog: oxidising and reducing.Oxidising smog is also called photochemical smog and it consists of high concentration of oxidants like ozone.Reducing smog contains high contents of SO2; it is chemically reducing by nature. It gets oxidised to SO3 first and then dissolves in water to form H2SO4 to produce acid rain.Therefore, option D is the correct answer.

• A. CuO + ZnO
• B. CuO + Cr2O3
• C. Al2O3 + ZnO
• D. ZnO + Cr2O3

Explanation: Industrially, the conversion of water gas (a mixture of carbon monoxide and hydrogen) into methanol is typically achieved using a catalyst known as a methanol synthesis catalyst. The most commonly used catalyst for this process is a mixture of copper (Cu) and zinc oxide (ZnO) promoted with aluminum oxide (Al₂O₃), often referred to as a copper-zinc catalyst. This catalyst operates under high-pressure conditions (around 50-100 atmospheres) and moderate temperatures (ranging from 200 to 300 degrees Celsius). The conversion of carbon monoxide and hydrogen to methanol occurs through a series of chemical reactions on the catalyst surface. The overall reaction can be represented by the following equation: CO + 2H₂ → CH₃OH The copper-zinc catalyst facilitates the hydrogenation of carbon monoxide, resulting in the formation of methanol. This process is known as the "methanol synthesis" and is widely used in the production of methanol for various industrial applications. Industrial preparation of methanol takes place by first purifying a mixture of CO and H2 gas (collectively called water gas), then compressing them at 200 atm and then passing them over a heated catalyst at 200℃. The catalyst used in the reaction chamber is a mixture of ZnO and CrO3. Methanol vapours are formed which are condensed to form methanol. Option D is correct. (Source: PCTB book 2, page 214)

• A. Polyester
• B. Epoxy resins
• C. Acrylic resins
• D. Polyamides

Explanation: In 1929, WH Carothers suggested classification of polymers based upon the way polymers are formed. In condensation polymerization, the monomers are joined together with the removal of a small molecule. They are generally ionic in nature. In addition polymerisation, the monomers are joined together without any removal and they have double bonds.Acrylic resins are used in the manufacture of plastics, paints for car industry and water based weather resistant paints. The common monomers are methyl methacrylate, acrylic acid and acrylonitrile. Each of these have double bonds where the monomers link together to form large chains of addition polymers. Therefore, option C is the correct answer.Structures of the monomers are shown below:(Source: PCTB book 2 page 272)

• A. Ribose
• B. 2 - deoxyribose
• C. 3 - deoxyribose
• D. 2 - deoxypentose

Explanation: The sugar unit in a DNA molecule is deoxyribose. Deoxyribose is a five-carbon sugar that forms the backbone of the DNA molecule along with phosphate groups. It is called "deoxyribose" because it lacks one oxygen atom compared to the ribose sugar found in RNA. The arrangement of deoxyribose and phosphate groups forms the alternating sugar-phosphate backbone of the DNA double helix, while the nitrogenous bases (adenine, thymine, cytosine, and guanine) are attached to the deoxyribose sugar. This is a factual recall question. DNA is a polymer of deoxyribonucleotides. The sugar is a pentose sugar called 2-deoxyribose, which differs from pentose ribose sugar by lacking an oxygen atom on carbon no. 2.

• A. Cross linked linear polymer
• B. Co polymer
• C. Homopolymer
• D. Condensation polymer

Explanation: The polymer formed by the polymerization of vinyl acetate (CH2=CHOOCCH3) is polyvinyl acetate (PVA), which is a homopolymer. A homopolymer is a polymer formed from a single type of monomer, in this case, vinyl acetate. The polymerization process involves the opening of the double bond in the vinyl acetate monomer and the formation of new single bonds between the monomers.

• A. Phenol
• B. Ethanol
• C. Butanol
• D. Methanol

Explanation: Bakelite is a condensation polymer of formaldehyde and phenol. In practice, the phenol and formaldehyde are first polymerized to a small extent by using the proper choice of catalyst and temperature.

• A. A polyamide
• B. A condensation polymer
• C. An addition polymer
• D. A polyester

Explanation: As you can see in the above image, polystyrene is an addition polymer, where the monomers (in this, a styrene molecule) are simply linked together to form a long chain, without the formation of a secondary product so, the answer is C. Option A describes polyamide, which is a condensation polymer formed by monomers, linked by amide bonds. Option B describes condensation polymers, where the functional groups of monomers are linked together, forming a secondary product, such as H2O, in the process. Option D describes a polyester, which is a condensation polymer, formed by monomers linked by ester linkages.

• A. Compounds
• B. Molecules
• C. Ions
• D. Elements

Explanation: Option A: Compounds, refer to substances that are formed by the combination of two or more different elements or compounds.Option B: Molecules are formed by the combination of two or more atoms, either of the same or different elements.Option C: Ions are formed by the gain or loss of electrons from atoms or molecules, resulting in a charged species. Allotropes, on the other hand, are different structural forms of the same element and do not involve the gain or loss of electrons to form ions.Option D: Allotropy, is the existence of a chemical element in two or more forms, which may differ in the arrangement of atoms in crystalline solids.