The identity matrix $I_n$ is a square matrix in which:

Question

Accepted Answer

C. Diagonal entries are $1$ and all off-diagonal entries are $0$

$I_n$ has $a_{ii} = 1$ for $i = 1, \dots, n$ and $a_{ij} = 0$ for $i 
e j$. Its key property is $AI = IA = A$ for any compatible matrix $A$. A matrix with all entries $1$ is a 'matrix of ones', not the identity.

Answer

All entries are $1$

Answer

All entries are $0$

Answer

Diagonal entries are $0$ and all off-diagonal entries are $1$