Why do transition elements have a greater tendency to form interstitial compounds?

Assertion $(A)$: While going from left to right in the periodic table,the atomic size decreases more rapidly for the $3d$-series compared to the $4f$-series of elements.
Reason $(R)$: $3d$-electrons experience lesser shielding than $4f$-electrons.

Why are transition elements less electropositive than the metals of group-$1$ and group-$2$?

Match the following aspects with the respective metal.

Aspects	Metal
$a$. The metal which reveals a maximum number of oxidation states	$i$. Scandium
$b$. The metal although placed in $3d$ block is considered not as a transition element	$ii$. Copper
$c$. The metal which does not exhibit variable oxidation states	$iii$. Manganese
$d$. The metal which in $+1$ oxidation state in aqueous solution undergoes disproportionation	$iv$. Zinc

Select the correct option.

Because of lanthanoid contraction,which of the following pairs of elements have nearly same atomic radii? (Numbers in the parenthesis are atomic numbers)

Which of the following has the highest ionic radii?