If ∠ADB of the rhombus ABCD is 30°, then ∠ACB =

1. 30°

2. 60°

3. 70°

4. 90°

In rhombus opposite sides are parallel. The diagonal BD acts as a transversal line.

Therefore, the alternate interior angles are equal.

∠DBC = ∠ADB = 30°

From figure,

∠OBC = ∠DBC = 30°

∠BOC = 90° [Diagonals of rhombus cut at right angles]

In triangle BOC,

∠OBC + ∠BOC + ∠OCB = 180°

30° + 90° + ∠OCB = 180°

120° + ∠OCB = 180°

∠OCB = 180° - 120°

∠OCB = 60°.

Hence, option 2 is the correct option.