O is center of the the circle and ∠AOB = 60°. The length of chord AB is :

1. equal to radius of the circle

2. equal to the side of a regular pentagon

3. bigger than the radius of the circle

4. smaller than the radius of the circle.

From figure,

⇒ OA = OB (Radius of same circle)

⇒ ∠OBA = ∠OAB = x (let) [In a triangle angles opposite to equal sides are equal.]

In △ AOB,

By angle sum property of triangle,

⇒ ∠OBA + ∠OAB + ∠AOB = 180°

⇒ x + x + 60° = 180°

⇒ 2x + 60° = 180°

⇒ 2x = 180° - 60°

⇒ 2x = 120°

⇒ x = $\dfrac{120°}{2}$ = 60°

⇒ ∠OBA = ∠OAB = ∠AOB = 60°.

∴ AOB is an equilateral triangle.

∴ AB = OA = OB

∴ AB = Radius of circle.

Hence, Option 1 is the correct option.