Question

reaction of metal with acid is an example of Oxidation reaction​

Answer 1

2 Mg(s) + O2(g) -----> 2 MgO(s)

Here oxidation of Mg take place .

Answer 2

Yes you are correct. The reaction of metal with acid is an example of oxidation reaction because in this hydrogen is reduced. For example:

$Zn + HCl ----> ZnCl + H2$

ZnCl is reduced