The set of all values of $\lambda$ for which the system of linear equations : $2x_1-2x_2+x_3 = \lambda x_1 \\2x_1 -3x_2+2x_3 = \lambda x_2 \\ -x_1 +2x_2 = \lambda x_3\\$ has a non- trivial solution ,

Question

$\begin{array}{1 1} \text{is a singleton } \\ \text{contains two elements} \\ \text{contains more than two elements} \\ \text{is an empty set} \end{array} $