b
The system of linear equations is:
$x+y+z=2$
$2x+y-z=3$
$3x+2y+kz=4$
As, system as unique solution.
So, $\begin{array}{*{20}{c}}
1&1&1\\
2&1&{ - 1}\\
3&2&k
\end{array} \ne 0$
$ \Rightarrow k + 2 - \left( {2k + 3} \right) + 1 \ne 0$
$ \Rightarrow k \ne 0$
Hence, $k \in R - \left\{ 0 \right\} \equiv S$