All Free Biology MCQs with Answers

• A. Sulfur
• B. Carbon
• C. Nitrogen
• D. Oxygen

Explanation: Chemically, proteins are complex nitrogenous organic compounds, which are associated with the concept of life itself.By chemical composition, proteins are composed of carbon, hydrogen, oxygen, and nitrogen. Some proteins also contain smaller quantities of sulfur and phosphorus.The percentage of nitrogen is fairly constant and is about 16% of the molecular weight of protein. Hence, C is the correct option.

• A. Catalyst
• B. Lipoproteins
• C. Conjugated molecules
• D. Biocatalyst

Explanation: Enzymes are proteins that catalyze a chemical reaction in our body. They function as a catalyst that speeds up the reaction by lowering the activation energy. The enzyme accelerates a chemical reaction without changing its equilibrium, so it is called as a biocatalyst.

• A. Oxidoreductase
• B. Hydrolases
• C. Ligases
• D. Transferases

Explanation: These enzymes, called transferases, move functional groups from one molecule to another.

• A. Forms a colloidal solution with water
• B. Is soluble in water
• C. Does not form an emulsion with the grease
• D. Forms an emulsion with the grease

Explanation: Soap has a tadpole like structure, because they possess a long carboxylic acid chain through which hydrocarbons and sodium-pottasium ions are attached. The ionic part dissolves in water whereas the non-ionic carbon chain dissolves in oil and forms an emulsion, but to form an emulsion, the non-ionic chain must have more than 8 carbon atoms.

• A. Glycerol and gum are added to the soap.
• B. The soap is dissolved in alcohol and then the alcohol is evaporated out.
• C. Glycerine is added to the alcoholic solution of soap.
• D. A saturated solution of sodium chloride is added to the soap.

Explanation: To make the soap transparent firstly soap crystals are processed with solvents like glycerine, alcohol and sugar to dissolve, that allowing light to pass through it, then further the solvent is evaporated by heating the solution therefore soap becomes transparent.

• A. Increased by both
• B. Reduced by both
• C. Reduced by detergent and increased by soap
• D. Reduced by soap and increased by detergent

Explanation: When soap and detergent are added to the water, the ionic part of soap and detergent attract grease and repel water molecules, thus the hydrogen bonds that hold the water molecules weaken therefore surface tension of water decreases.

• A. It increases the hardness of soap
• B. It increases the solubility of soap in water
• C. It decreases the solubility of soap in water
• D. It decreases the surface tension of water

Explanation: The solubility of soap in water depends upon the non-ionic or carbohydrate part of soap, as the sodium chloride is added in the hot process of preparation of soap the ionic part of soap increases therefore solubility of soap in water decreases.

• A. Soaps and detergents both are used only in soft water
• B. Soaps and detergents both are used in soft as well as hard water.
• C. Soap is used only in soft water while detergent can be used in soft as well as hard water
• D. Detergent is used only in soft water while soap is used in soft and hard water, both

Explanation: Sodium-potassium ions that are present in the ionic part of soap form scum with calcium and magnesium ions of hard water and get precipitated whereas calcium and magnesium salts of detergent are soluble in water. Thus soap forms lather only in soft water whereas detergent forms lather in both soft and hard water.

• A. Gasoline
• B. Potassium palmitate
• C. Soap
• D. Potassium pentanoate

Explanation: Potassium pentanoate does not have cleaning property because it has less than 8 carbon atoms. wheras all other compounds have cleaning property due to presence of long carbon chain.

• A. Caustic potash
• B. Glycerine
• C. Potassium glycolate
• D. Potassium stearate

Explanation: Bathing soap are Na+ or K+ salts of carboxylic acid. Potassium stearate is K+ salt of carboxylic acid (C17H35CO2K).