Which of the following matrices are nilpotent?
(0100)\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}(0010)
(1001)\begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}(1001)
(0500)\begin{pmatrix} 0 & 5 \\ 0 & 0 \end{pmatrix}(0050)
(1100)\begin{pmatrix} 1 & 1 \\ 0 & 0 \end{pmatrix}(1010)