Correct answer is B. Hydrogen
Copper will not react with dil. HCl.
Mg is highly reactive with dil. HCl.
Mg + 2Hcl \(\longrightarrow\) H2 + Mgcl2.
A cracking sound is heard as hydrogen burns.
When dil. HCl is added to Fe, then ferrous chloride (FeCl2) and hydrogen gas (H2) will be formed.
2HCl + Fe \(\longrightarrow\) FeCl2 + H2.