Question

why in reaction of acid and base hydrogen gas evovled

Answer 1

Acid contains $<u>hydrogen atoms</u>$ and \:Bases\: contains $<u>hydroxide atoms .</u>$
If we add Acid and Base then,
$<b><i>Acid+Base ----> Salt+Hydrogen gas </i></b>$
For example-
$<b><i>HCl + NaOH ----> NaCl + H2</i></b>$
here, $<u>NaOH is base <> HCl is acid <> NaCl is a salt </u>$