What type of matrix is (A=\begin{bmatrix}1&0\\0&1\end{bmatrix})?

Correct answer: Identity matrix

The governing definition of an identity matrix is a square matrix whose main-diagonal entries are 1 and whose off-diagonal entries are 0. In the given 2 × 2 matrix, both diagonal entries are 1, while the two entries away from the main diagonal are 0. Therefore it is the 2 × 2 identity matrix, usually written I₂, so option B is correct. It is not a zero matrix because its diagonal entries are not zero. It is not a row matrix because it has two rows, and although every square matrix is technically rectangular in a broad sense, “rectangular matrix” in this question is not the specific classification represented by the displayed form.