As we know that, any square matrix of order n is said to be idempotent matrix if A2=A. So, A - 4. Similarly, as we know that, a square matrix of order n is said to be nilpotent matrix if there exists least positive integer m such that Am=O, where O is the null matrix of order n. So, B - 1. Similarly, as we know that, a square matrix of order n is said to be involuntary matrix if A2=I, where I is the identity matrix of order n. So, C - 2. As we know that, if A is a real square matrix such that A = A’ then A is said to be a symmetric matrix. So, D - 3. Hence, option D is the correct answer