Let $A=\left(\begin{array}{ccc}0 & 0 & -1 \\ 0 & -1 & 0 \\ -1 & 0 & 0\end{array}\right)$, then

• A

  A is a null matrix
• B

  A is skew symmetric matrix
• C

  $\mathrm{A}^{-1}$ does not exist
• Correct answer
  D

  $A^2=1$

Hence, the correct answer is option: 'D'.