Consider the following two experimental set ups.

In both the assembles, the common product formed is

1) Metals react with acids produce hydrogen gas.

2) Reaction of base with metals it produce salt and hydrogen gas.

Zinc is more reactive than Hydrogen and it displaces Hydrogen from dilute acids.

Only few metals like Zn and Al reacts with bases like NaOH, KOH forms ${\text{H}}_{\text{2}}$  gas. 

$\text{Zn}+\text{2HCl}\to {\text{ZnCl}}_{\text{2}}+{\text{H}}_{\text{2}}\uparrow$ .

$Zn+2NaOH\to \underset{SodiumZincate}{N{a}_{2}Zn{O}_2}+H_2\uparrow$