If [1 2 3] A =[4 5], then the order of matrix A is :

The correct answer is Option (3) → $3×2$

$\begin{bmatrix}1&2&3\end{bmatrix}_{1×3}$

$A_{p×q}=\begin{bmatrix}4&5\end{bmatrix}_{1×2}$

from this we infer that

$p=3$ and $q=2$

so order (A) = $p×q$

$=3×2$