Question

A metal m does not liberate hydrogen from acids but reacts with oxygen to give a black colour product identity m
(1)na(2)mg(3)cu(4)ca

Answer 1

The correct option is 3-- coppe--Cur
Explanation:
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Metal m is copper which does not liberate H2 when it reacts with HCl acid as copper is least reactive than Hydrogen . So it cannot displace hydrogen from HCl.

Copper reacts with oxygen to form copper (II) oxide which is black in colour.
2Cu+ O2 ----->2CuO
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Answer 2

The answer of your question is copper "Cu". Because while reacting with oxygen it give the black product named as Copper oxide 
2Cu + O2 ⇒ 2CuO

 While the copper don't react with the HCl because of it being a higher reduction potential substance than the hydrogen. And only the metal with their reduction potential less than H2 have the ability to displace hydrogen and react with non-oxidizing acids just like the HCl.
Hope this help you.