Which of the following figures is the odd one out?

The correct answer is Option (2) → 

Look at the kind of lines. Three figures each have a curved line (a circle) as well as straight lines. Option (2), a rectangle with a small square inside, is made of straight lines only, so it is the odd one out.

Option (1) — Incorrect. A heptagon (seven-sided figure) with a small circle inside: it has a curved line (a circle).

Option (3) — Incorrect. A triangle with a small circle inside: it has a curved line (a circle).

Option (4) — Incorrect. An octagon with a small circle inside: it has a curved line (a circle).