What is the observed electronic configuration of $Cu$?

What is the correct order of the theoretical magnetic moment for $Mn^{2+}$,$Cr^{2+}$,and $V^{2+}$?

Assertion $(A)$: $Mo$ has the ground state electronic configuration $4d^5 5s^1$.
Reason $(R)$: $Mo$ has the highest exchange energy among the second row transition elements.
The correct option among the following is:

Match the following:

List-$I$ (Element)	List-$II$ (Block)
$A$. $Cd$	$I$. $f$-block
$B$. $Eu$	$II$. $s$-block
$C$. $Se$	$III$. $d$-block
$D$. $Ba$	$IV$. $p$-block

The correct answer is:

In which of the following is variable valency observed?

Identify the set of paramagnetic ions among the following.