Given : The vertices of tetrahedron are
P(-1, 2, 0), Q(2, 1, -3), R(1, 0, 1) & S(3, -2, 3)
$\therefore$ Volume of tetrahedron $= \ \frac{1}{6} \ [\vec{PQ} \ \vec{PR} \ \vec{PS}]$
Now,
$\vec{PQ}=(2+1)\hat{i}+(1-2)\hat{j}+(-3)\hat{k}=3\hat{i}-\hat{j}-3\hat{k}$
Similarly, $\vec{PR}=2\hat{i}-2\hat{j}+\hat{k}$
$\& \ \ \ \ \ \vec{PS}=4\hat{i}-4\hat{j}+3\hat{k}$
$\therefore $ Volume of tetrahedron
$=\frac{1}{6} \begin{vmatrix}
3 & -1 & -3\\
2 & -2 & 1 \\
4 & -4 & 3 \end{vmatrix} =\frac{2}{3}$