d
(d)${a_{ji}} = {i^2} - {j^2}$ is a square matrix. For a skew symmetric matrix ${a_{ji}} = -{a_{ji}}$
$\Rightarrow$ ${a_{ij}} = {i^2} - {j^2}$ and ${a_{ji}} = {j^2} - {i^2}$
$\Rightarrow$ ${a_{ij}} + {a_{ji}} = 0 $
$\Rightarrow \,{a_{ij}} = - {a_{ji}}$
Hence, $ {a_{ji}}$ is a skew symmetric matrix.