A square matrix $\left[{\mathrm{a}}_{\mathrm{ij}}\right], {\mathrm{a}}_{\mathrm{ij}}=0$ for $\mathrm{i}\ne \mathrm{j}$ and ${\mathrm{a}}_{\mathrm{ij}}=\mathrm{k}$ (constant) for i = j is called a

   In a scalar matrix all the principle diagonal elements are same & remaining elements are Zero.

$$\begin{gathered} \therefore {\mathrm{a}}_{\mathrm{ij}}=\mathrm{K}, \mathrm{for} \mathrm{i}=\mathrm{j} \\ \therefore \mathrm{A} \mathrm{is} \mathrm{a} \mathrm{scalar} \mathrm{matrix} \end{gathered}$$