Study the reaction. 2AgNO3 (aq)+Cu (s)→Cu(NO3)2 (aq)+2Ag (s)
If the oxidation number of copper changes from 0 to +2, is this a redox reaction?
-No; copper gained 2 electrons and was reduced.
-Yes; copper lost 2 electrons and was oxidized.
-Yes, the products have 2 fewer electrons than the reactants.
-No, the products have as many electrons as the reactants.

If the oxidation number of copper changes from 0 to +2 then yes this is a redox reaction as copper lost 2 electrons and was oxidized.

Explanation:

When an element or atoms loses an electron then it acquires a positive charge.

This charge on an atom represents its oxidation state.

For example,

Here, oxidation number of copper changes from 0 to +2.

A redox reaction in which electrons are removed from an atom or a reaction where an increase in oxidation number of an atom takes place is called oxidation-half reaction. The atom itself gets oxidized.

This means that here copper lost 2 electrons and was oxidized.

Thus, we can conclude that if the oxidation number of copper changes from 0 to +2 then yes this is a redox reaction as copper lost 2 electrons and was oxidized.

the answer is definitely c.