Question

Which of the following ions has the smallest radius?
A. $T{i^{2 + }}$
B. $P{t^{2 + }}$
C. $N{i^{2 + }}$
D. $Z{n^{2 + }}$

Answer 1

Hint: In the question, we have ions of different elements so, we will compare their ionic radius. Ionic radius can be defined as the distance between the nucleus of ions to the ions of the outermost shell. Ionic radius increases down the group whereas along the period it decreases then increases and then again decreases.

Complete step by step answer:
Let us discuss the given options one by one.
$T{i^{2 + }}$
Titanium is an element with atomic number 22, it belongs to the period 4 and group 4. As we know, from the periodic properties of elements, the ionic radii decrease from group 1 to group 14 elements having positive ions. The nuclear charge increases with the increase in atomic number across the period.
$P{t^{2 + }}$
Platinum is an element with atomic number 78 and it belongs to group 10 and period 6. It has a maximum ionic radius among the given options as it has two more electron shells than the other ions given in the question.
$N{i^{2 + }}$
Nickel is an element with atomic number 28 and it belongs to group 10 and period 4. Here, we can say it will have a minimum radius as it is the first element of group 10. Along the period also the ionic radius for nickel decreases.
$Z{n^{2 + }}$
Zinc is an element with atomic number 30 and it belongs to group 12 and period 4. It has an ionic radius greater than nickel as in its electronic configuration 3d orbitals are filled. The filled orbitals show interelectronic repulsion.
So, in the end, we can conclude that nickel ions have a minimum radius.

So, the correct answer is Option C.

Note: While comparing the ionic radius, we should consider all the points. If we compare according to the increase and decrease along with the period and group then zinc should have a smaller radius than a nickel. In consideration with the d filled orbital, it has a greater radius.
Down the group, the ionic radius increases due to an increase in energy levels and the attraction between the nucleus and electrons from the outer shell also increases.