All Free Everyday Science MCQs with Answers

521. Which of the following is the most toxic gas?

• A. Carbon dioxide
• B. Carbon monoxide
• C. Nitrogen
• D. Hydrogen

Explanation: Carbon monoxide is highly toxic because it binds haemoglobin strongly and prevents blood from carrying oxygen. Nitrogen and hydrogen are not poisonous at ordinary concentrations, while carbon dioxide is mainly dangerous at high concentrations.

522. Which one of the following gases is readily soluble in water at room temperature?

• A. Chlorine
• B. Nitrogen
• C. Ammonia
• D. Carbon dioxide

Explanation: Ammonia dissolves very readily in water and forms an alkaline solution called ammonium hydroxide in traditional descriptions. Nitrogen is only slightly soluble, and carbon dioxide is much less soluble than ammonia.

523. Bleaching powder contains___________?

• A. Nitrogen
• B. Iodine
• C. Chlorine
• D. Bromine

Explanation: Bleaching powder is commonly represented as calcium oxychloride, CaOCl₂, so its characteristic active element is chlorine. Chlorine is released in reactions and produces the bleaching effect.

524. Bleaching action of chlorine is by________?

• A. Oxidation
• B. Reduction
• C. Decomposition
• D. Hydrolysis

Explanation: Chlorine bleaches coloured substances by oxidation, destroying the chemical groups responsible for colour. Reduction, decomposition, and hydrolysis are not the main bleaching mechanism.

525. What is a mixture of Potassium Nitrate Powdered Charcoal and Sulphur called?

• A. Paint
• B. Glass
• C. Gun Powder
• D. Cement

Explanation: Gunpowder is a mixture of potassium nitrate, powdered charcoal, and sulphur. Potassium nitrate supplies oxygen during burning, while charcoal and sulphur act as fuels.

526. Nail polish remover contains___________?

• A. Acetone
• B. Benzene
• C. Acetic acid
• D. Petroleum ether

Explanation: Most nail-polish removers contain acetone, a solvent that dissolves the film-forming compounds in nail polish. Acetic acid is vinegar and is not the usual nail-polish remover solvent.

527. Which one of the following is the softest?

• A. sodium
• B. iron
• C. aluminium
• D. lithium

Explanation: Sodium is softer than lithium because alkali metals generally become softer down the group. Iron and aluminium are much harder metals.

528. Which variety of glass is heat resistant?

• A. Bottle glass
• B. Flint glass
• C. Hard glass
• D. Pyrex glass

Explanation: Pyrex is borosilicate glass, whose low thermal expansion allows it to withstand sudden temperature changes. Ordinary bottle and flint glasses are more likely to crack under thermal shock.

529. Which synthetic fibre is known as artificial Silk?

• A. Nylon
• B. Rayon
• C. Cotton
• D. Terylene

Explanation: Rayon is made from regenerated cellulose and has a silk-like appearance and feel, so it is called artificial silk. Nylon and terylene are synthetic fibres but do not traditionally carry this name.

530. The alloy of aluminium used for making magnet is_________?

• A. Duralumin
• B. Y-Alloy
• C. Alnico
• D. Aluminium bronze

Explanation: Alnico contains aluminium, nickel and cobalt and is used to make permanent magnets. Duralumin and Y-alloy are aluminium alloys designed mainly for strength and lightness.