WHEN METALS REACT WITH ACIDS:-
Metals react with acids to give salt and hydrogen gas.
Metal + Dilute acid → Salt + Hydrogen
2Na(s) + 2HCl(aq) → 2NaCl(aq) + H2(g)
Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
The reactivity or activity series is a list of metals arranged in the order of their decreasing activities. The reactivity decreases in the order
Mg > Al > Zn > Fe