The electronic configuration of copper $({_{29}}Cu)$ is

Which forms interstitial compounds?

Match List-$I$ with List-$II$

List-$I$ Species	List-$II$ Electronic distribution
$A$. $Cr^{2+}$	$I$. $3d^8$
$B$. $Mn^{+}$	$II$. $3d^3 4s^1$
$C$. $Ni^{2+}$	$III$. $3d^4$
$D$. $V^{+}$	$IV$. $3d^5 4s^1$

Choose the correct answer from the options given below:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Generally, $3d$ transition metals have high melting points.
Reason $R$: Involvement of $3d$-electrons in addition to $4s$-electrons in the interatomic metallic bonding.
In light of the above statements, choose the most appropriate answer from the options given below:

The second and third rows of transition elements resemble each other much more than they resemble the first row. Explain why?

Which of the following triads has approximately equal size?