If all the elements of \(3\times 3\) matrix \(A\) are \(1\), then \(A^2-3A\) is

a null matrix a unit matrix a column matrix a diagonal matrix

a null matrix

$A=\begin{bmatrix}1&1&1\\1&1&1\\1&1&1\end{bmatrix}$ $A^2=\begin{bmatrix}3&3&3\\3&3&3\\3&3&3\end{bmatrix}$ so $A^2=3A$ $⇒A^2-3A=0$