Which element is most likely to form a cation?
a) sodium
b) silicon
c) sulfur
d) argon

Sodium

Explanation:

Sodium is alkali metal. All metal form cation by losing their valance electrons.

Sodium is member of group one it has one valance electron. It easily lose the electron and get stable electronic configuration by completing the octet.

When an atom lose electron cation is formed and when it gain electron anion is formed.

So sodium atom when lose its one valance electron it form cation with charge of +1.

While argon already have complete octet it can not form ion.

while valency of silicon is four and it form four covalent bond easily.

While sulfur form anion by gaining the electrons.

the answer is option a.