Which pair of elements with the given atomic numbers is expected to have similar properties?

Elements that lie in the same vertical column (group) of the periodic table possess the same number of valence electrons. Hence they display closely similar physical and chemical properties.

To decide which given pair belongs to the same group, write (or recall) their symbols and positions.

Checking each option

Option A : $$40 \;(Zr)$$ and $$72 \;(Hf)$$
Zirconium, $$Z = 40$$ : electronic configuration $$[Kr]\;4d^{2}\,5s^{2}$$
Hafnium, $$Z = 72$$ : electronic configuration $$[Xe]\;4f^{14}\,5d^{2}\,6s^{2}$$
Both end in $$d^{2}s^{2}$$, i.e. they have the outer-shell configuration $$ns^{2}(n-1)d^{2}$$, which places them in Group 4 (earlier notation 4B). Thus they are congeners and expected to show very similar properties. (The well-known lanthanide contraction keeps the size of Hf almost the same as Zr, making their resemblance even closer.)

Option B : $$20 \;(Ca)$$ is in Group 2 (alkaline-earth metals) whereas $$36 \;(Kr)$$ is a noble gas in Group 18 → different groups, dissimilar.

Option C : $$10 \;(Ne)$$ is a Group 18 noble gas; $$28 \;(Ni)$$ is a Group 10 transition metal → different groups, dissimilar.

Option D : $$11 \;(Na)$$ lies in Group 1 and $$12 \;(Mg)$$ in Group 2 → adjacent groups, not similar enough.

Hence the only pair expected to have similar properties is

Option A which is: $$40, 72$$.