Answer
$I_{n}$ is an $n\times n$ matrix that
has 1s down the main diagonal from upper left to lower right
and 0s elsewhere.
Work Step by Step
The multiplicative identity matrix $I_{n}$ is an $n\times n$ matrix such that
$AI_{n}=I_{n}A=A$
for all n$\times$n matrices.
$I_{n}$ is an $n\times n$ matrix that
has 1s down the main diagonal from upper left to lower right
and 0s elsewhere.
