Which of the following is an example of a chemical change?
A. Melting of wax
B. Cutting of wood
C. Burning of candle
D. Freezing of water
Answer: Option C
Solution (By JKExamLibrary)
Burning of a candle involves combustion of wax (hydrocarbons) with oxygen to produce CO₂ and H₂O, a chemical change. The melting of wax is a physical change. Cutting wood is physical (size change). Freezing water is physical (state change). A chemical change results in new substances with different properties. Often irreversible.
Explanation:
Graham's law: r₁/r₂ = √(M₂/M₁). Given rA/rB = 1/2, so √(MB/MA) = 1/2. Squaring: MB/MA = 1/4 => MB = MA/4 = 64/4 = 16 g/mol. B is lighter and diffuses faster. Logical check: rate inversely proportional to square root of molar mass; if rate is double, mass is quarter. Answer is 16.
Explanation:
Chlorine forms hypochlorous acid (HOCl) which is a strong oxidizing agent that destroys bacteria and viruses. It does not remove particles (filtration does) or dissolved salts.
Explanation:
Ammonium chloride (NH₄Cl) consists of NH₄⁺ and Cl⁻ ions. Ionic bond between NH₄⁺ and Cl⁻. Within NH₄⁺, N-H are covalent bonds, with one coordinate bond formed by donation of N's lone pair to H⁺. So all three bond types are present. NaCl purely ionic. CO₂ purely covalent. CH₄ purely covalent.
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