If Aufbau rule is not followed, K – 19 will be
placed in the block

We know that the Aufbau principle states that electrons fill lower energy atomic orbitals before filling higher-energy ones.

So, According to Aufbau principle electronic configuration of $\mathrm{K}-19$ will be 

$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^1$

Now, electronic configuration of $\mathrm{K}-19$ If Aufbau rule is not followed

$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^1$

the last-filling electron goes into d-orbital. so it will belong to d-block elements.

Hence, option(c) is the answer.