Which gas is released when acid reacts with metals?

The correct option is A

Hydrogen

An acid reacts with a metal and gives a salt with evolution of hydrogen gas.
$\text{Acid}+\text{metal}\to \text{salt}+{\text{H}}_2$

Many reactive metals like sodium, potassium, etc. displace hydrogen from acids.

$2HCl+2Na\to 2NaCl+H_2$