The correct order of decreasing third ionisation enthalpy of $Ti$,$V$,$Cr$,and $Mn$ is:

Many transition metals form interstitial compounds. The characteristics of these interstitial compounds are:
$I$. They have high melting points,higher than those of pure metals.
$II$. They are very hard.
$III$. They retain metallic conductivity.
$IV$. They are chemically more reactive than the pure metals.

Fill in the blanks:
$(a)$ The shielding effect of $d$-electrons is ......... effective than $p$-electrons.
$(b)$ $A$ decrease in exchange energy leads to a ......... in stability.
$(c)$ The maximum oxidation state of $Mn$ is ..........
$(d)$ The stability of $Mo(VI)$ and $W(VI)$ is found to be .......... than that of $Cr(VI)$.

Which of the following statements is correct?

Find the value of spin-only magnetic moment for chromium cation in $+2$ state. (in $BM$)

Which one of the following characteristics of the transition metals is associated with their catalytic activity?