Give the behaviour of marginal product and total product as more and more units of only one input are employed while keeping other inputs as constant.

This is law of variable proportion. The law of variable proportion states that if we keep on increasing the units of variable factor (labour) with a fixed factor (Land), the behaviour of total product and marginal product is listed below –

Behaviour of Total Product - The total product increases at an increasing rate in the beginning, then increases at a diminishing rate and after a particular level of output it ultimately falls.

Behaviour of Marginal Product - The marginal product increases in the beginning, then it starts falling but remains positive and ultimately it continues to fall and also become negative.

It can be explained with the help of following table and graph.