Question

The time period of a particle in simple harmonic motion is equal to the time between consecutive appearances of the particle at a particular point in its motion. This point is ​? answer is extreme position ​​please explain what the question is trying to say

Answer 1

In a simple harmonic motion of a particle (about its mean position) the particle oscillates between two extreme positions.

In one time period, the particles passes through (ie., crosses) the extreme point exactly once...   But it passes through (crosses) all other points twice.

That is the reason for choosing the extreme point as the reference in the question above.

Answer 2

In one time period, the particles passes through (ie., crosses) the extreme point exactly once...   But it passes through (crosses) all other points twice.

That is the reason for choosing the extreme point as the reference in the question above.