Transition elements show high melting points. Why?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$ $Cu^{2+}$ in water is more stable than $Cu^{+}$.
Reason $(R):$ Enthalpy of hydration for $Cu^{2+}$ is much less than that of $Cu^{+}$.
In the light of the above statements,choose the correct answer from the options given below:

The stability of a particular oxidation state of a metal in an aqueous solution can be determined by:

Given below are two statements $:$
Statement $I : CrO_3$ is a stronger oxidizing agent than $MoO_3$
Statement $II : Cr(VI)$ is more stable than $Mo(VI)$
In the light of the above statements,choose the correct answer from the options given below.

The electronic configuration of $Cr^{3+}$ is

Which element of the $3d$-series has the highest third ionisation enthalpy?