Q.

If the product of two matrices is a zero matrix, then:

1 at least one of the matrix is a zero matrix  
2 both the matrices are zero matrices  
3 it is not necessary that one of the matrices is a zero matrix  
4 None of the above  

Ans.

(3)

Ans.       it is not necessary that one of the matrices is a zero matrix

Explanation:

Let  A=[0-102]  and  B=[3500]

Then,  AB=0  but A and B are non-zero.