Assign reason for each of the following : (i) Manganese exhibits the highest oxidation state of $+7$ among the 3d series of transition elements. (ii) Transition metals and their compounds are generally found to be good catalysts in chemical reactions. (iii) $\text{Cr}^{2+}$ is reducing in nature while with the same d-orbital configuration $(d^4)$ $\text{Mn}^{3+}$ is an oxidising agent. (iv) $\text{Zn}$ has lowest enthalpy of atomization. (v) $\text{Cu}^+$ is unstable in an aqueous solution.