Question

_____ matrix is a square matrix in which all the elements other than the principal diagonal elements are zero.

• A. scalar
• B. null
• C. diagonal
• D. unit

Answer 1

The correct option is C diagonal

A diagonal matrix is a square matrix in which all the elements other than the principal diagonal elements are zero.

Unit matrix and scalar matrix are special case of a diagonal matrix.

A diagonal matrix, in which all diagonal elements are equal to same scalar, is called a scalar matrix.

A diagonal matrix, in which all diagonal elements are equal to one, is called a unit matrix.

Example: Diagonal matrix in $2\times 2$ form.
$\left[\begin{array}{cc}1& 0\\ 0& 3\end{array}\right]$

So, only Option C is the correct answer.

As unit matrix and every scalar matrix is a diagonal matrix, but every diagonal matrix need not to be unit matrix and scalar matrix.