b
$A =\left[\begin{array}{cc}1+ i & 1 \\ - i & 0\end{array}\right]$
$A ^{2}=\left[\begin{array}{cc}1+ i & 1 \\ - i & 0\end{array}\right]\left[\begin{array}{cc}1+ i & 1 \\ - i & 0\end{array}\right]$
$A ^{2}=\left[\begin{array}{cc} i & 1+ i \\ - i +1 & - i \end{array}\right]$
$A ^{4}=\left[\begin{array}{cc} i & 1+ i \\ - i +1 & - i \end{array}\right]\left[\begin{array}{cc} i & 1+ i \\ - i +1 & - i \end{array}\right]$
$A ^{4}=\left[\begin{array}{cc}1 & 0 \\ 0 & 1\end{array}\right]= I$
$A ^{4 n +1}= A$
$n =1,5,9, \ldots \ldots, 97$
$\Rightarrow$ total elements in the set is $25 .$