Which of the following matrices is diagonal but not scalar?

\begin{bmatrix}2 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & 5\end{bmatrix}

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\begin{bmatrix}2 & 0 & 0 \\ 0 & 2 & 0 \\ 0 & 0 & 2\end{bmatrix}

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\begin{bmatrix}2 & 0 & 1 \\ 0 & -1 & 0 \\ 0 & 0 & 5\end{bmatrix}

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\begin{bmatrix}0 & 0 & 2 \\ 0 & -1 & 0 \\ 5 & 0 & 0\end{bmatrix}

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CorrectNot quiteAnswer A

Correct answer: A

Every element off the leading diagonal is 0, and the diagonal elements are not all equal.
Only $\begin{bmatrix}2 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & 5\end{bmatrix}$ fits.

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Explanation