Acids, Bases and Salts MCQs

Q1. Which of these is an olfactory indicator (NCERT)?

• A.phenolphthalein
• B.vanilla extract
• C.methyl orange
• D.litmus

Answer: B. vanilla extract

Quick parse - a typical chemistry numerical. We are after the quantity the stem asks for. Tool of choice - F = m*a, V = I*R, n = m/M, v = f*lambda, KE = (1/2) m v^2). Rearrange it for the unknown before substituting. Numbers in: F = m*a, V = I*R, n = m/M, v = f*lambda, KE = (1/2) m v^2). Common-sense check: recall the defining law / equation for the named quantity (e.g. Lock in option B) vanilla extract. Trap-watch: option A) 'phenolphthalein' is incorrect: It changes colour, not odour; option C) 'methyl orange' is incorrect: Methyl orange changes colour, not smell.

Q2. Which gas is released when an acid reacts with an active metal like zinc?

• A.Hydrogen
• B.CO2
• C.Chlorine
• D.Oxygen

Answer: A. Hydrogen

NCERT fact (chemistry, chapter 'Acids, Bases and Salts'): Acid + metal -> salt + hydrogen (H2 gas, pops with a burning splint). Why option A fits - Correct. Distractor analysis: option B) 'CO2' doesn't hold - CO2 comes from acid + carbonate, not metal; option C) 'Chlorine' is wrong because No Cl2 evolved unless electrolysis. Final answer - A) Hydrogen.

Q3. Which of the following is an olfactory indicator?

• A.Onion
• B.Litmus
• C.Methyl orange
• D.Universal indicator

Answer: A. Onion

Asked for the unknown; data is laid out in the stem. By F = m*a, V = I*R, n = m/M, v = f*lambda, KE = (1/2) m v^2). F = m*a, V = I*R, n = m/M, v = f*lambda, KE = (1/2) m v^2). recall the defining law / equation for the named quantity (e.g. Consequently option A) Onion. Others fail: option B) 'Litmus' fails since Litmus is a colour (not smell) indicator; option C) 'Methyl orange' is wrong because It changes colour, not odour.