Which of the following is A, M, and N for the given observation?

Ramesh dropped a metal piece ‘A’ in the solution of another metal ‘M’. After some time a new colourless compound ‘N’ is formed.

A is $\mathit{Zn}$, M is$\mathit{ ZnS}{O}_4$ and N is $\mathit{CuS}{O}_4$ for the given observation.
According to the reactivity series, Zn is more reactive than copper. A is metal so let’s consider A as zinc, and the solution of another metal, M, can be $\mathit{CuS}{O}_4$ because when N is formed after the reaction, it is colourless, so it can be $\mathit{ZnS}{O}_4$ which is colourless. The reaction is a single displacement reaction. 
$\mathit{Zn}+\mathit{CuS}{O}_4\to \mathit{ ZnS}{O}_4+\mathit{Cu}$.

Hence, it is clear that A is $\mathit{Zn}$, N is $\mathit{CuS}{O}_4$  and M is $\mathit{ZnS}{O}_4$.