Question

A metal reacts with acid and liberates gas which burns with a pop sound when brought in contact with a flame.

• A. nitrogen
• B. carbon monoxide
• C. hydrogen
• D. carbon dioxide
• E. oxygen

Answer 1

The correct option is C hydrogen

Metals on reaction with acids liberate hydrogen gas.
For example: $Mg+2HCl\to MgC{l}_2+H_2$.

When a small flame can be brought near to the gas it puts off with a pop sound. The pop sound comes from the tiny explosion that occurred due to the burning of hydrogen with oxygen.
Other mentioned gases, do not burn with oxygen, so will not give the pop sound.