Answer: Option B
:
B
A regular polygon is a polygon which is equiangular i.e. all the angles are equal and equilateral i.e. all the sides are equal.
The triangle if equilateral is a regular polygon. If not, it is not a regular polygon.
A rhombus has equal sides but not equal angles.
A Rectangle has equal angles but not equal sides. Hence, they are not regular polygons.
A square has equal sides and equal angles. Hence, it is a regular polygon.