At the point where TP is at its maximum, MP = 0, the point at which it crosses the x- axis. After this point, MP is actually negative, meaning that TP is falling.

What happens to MP when TP falls?

Relationship between Total Product and Marginal Product

When TP increases at a diminishing rate, MP declines. This continues till the point where TP is at its highest. When TP reaches its maximum point, MP becomes zero.

When TP starts falling then MP becomes?

TP, MP, AP: Shape of the Curves

Here, MP =0. After the maximum, TP starts to fall or it declines. The MP curve also initially increases, reaches its maximum and then declines. Note that the maximum of MP is reached at the point where TP starts to increase at a diminishing rate.