Total product (TP) increase up to maximum and then it starts falling. This is due to the law of diminishing marginal product.

When total product (TP) is maximum, marginal product (MP( is zero. Marginal product is the slope of the total product curve.

When TP is raising MP is positive and when TP is falling, marginal product is negative.

Average product (AP) reaches its maximum when it meets the marginal product curve, beyond which average product falls.

Average product would fall but would never be equal to zero as is the case for marginal product. This is because output is never zero.