Which element from the following exhibits a common oxidation state of $+2$ only?

The stability of $Cu^{2+}$ is more than $Cu^{+}$ salts in aqueous solution due to -

Silver atom has completely filled $d$ orbitals $\left(4d^{10}\right)$ in its ground state. How can you say that it is a transition element?

The correct order of $E^{\circ}_{M^{2+}/M}$ values for the four successive elements $Cr$,$Mn$,$Fe$,and $Co$ is:

Four successive members of the first series of the transition metals are listed below. For which one of them is the standard electrode potential $(E^o_{M^{2+}/M})$ value positive?

Out of $Cu_{2}Cl_{2}$ and $CuCl_{2}$,which is more stable and why?