A diagonal of a rectangle is inclined to one side of the rectangle at 35°.

Given: In rectangle ABCD, ∠OAD = 35°.

Since, ∠BAD = 90°

⇒">⇒⇒ ∠OAB = 90° -">−- 35° = 55°

In ΔOAB,

Since, OA = OB      (Diagonals of a rectangle are equal and bisect each other)

⇒">⇒⇒ ∠OAB = ∠OBA = 55°     (Angles opposite to equal sides are equal)

Now, in ΔODA,
 
55° + 55° + ∠DOA = 180°       (Angle sum property of a triangle)

⇒">⇒⇒ ∠DOA = 180° -">−- 110°

⇒">⇒⇒ ∠DOA = 70°

Thus, the acute angle between the diagonals is 70°.

Hence, the correct option is (b).