The acceleration is zero when:

An object is suspended vertically from an ideal spring.

The spring is initially in its relaxed position. The object is then released and oscillates about the equilibrium position. Answer choices for Questions 1–4:
(a) The spring is relaxed.
(b) The object is at the equilibrium point.
(c) The spring is at its maximum extension.
(d) The spring is somewhere between the equilibrium point and maximum extension.