Question

Which of these reactions release a gas which burns with a pop sound?

• A. $CaC{O}_3+H_{2}S{O}_4$
• B. $Cu+HCl$
• C. $K+HCl$
• D. $NaOH+H_{2}S{O}_4$

Answer 1

The correct option is C $K+HCl$

Only metals above hydrogen in the reactivity series react with a dilute acid to form hydrogen gas, which burns with a pop sound.

Potassium is above hydrogen in the reactivity series, so potassium releases hydrogen upon reaction with $HCl$.
$K+HCl\to KCl+H_2$

Copper is below hydrogen in the series. So, Cu does not release hydrogen on its reaction with hydrochloric acid.

$NaOH$ is a base which participates in a neutralisation reaction with sulphuric acid to form salt and water.

The reaction between $CaC{O}_3$ and sulphuric acid produces carbon dioxide gas which doesn't burn. So it can't make a pop sound.