(c)
The correct electron dot structure shows each Cl atom with 3 lone pairs and 1 shared pair between them, satisfying the octet of both chlorine atoms (valency = 1).
Chlorine has 7 valence electrons. Each Cl needs 1 more electron to complete its octet, so it shares one electron with the other Cl, forming a single covalent bond with 3 lone pairs on each atom. The option showing exactly this arrangement is correct. In MCQs, quickly count the dots: each Cl should have 6 dots (3 pairs) + 1 shared pair between them.