[tex]n=\frac{V}{V_{0}}\\\\
V=48dm^{3}\\
V_{0}=22.4\frac{dm^{3}}{mol}\\\\
n=\frac{48dm^{3}}{22.4\frac{dm^{3}}{mol}}\approx2mol\\\\
n=\frac{m}{M_{r}} \ \ \ \Rightarrow \ \ \ M_{r}=\frac{m}{n}\\\\
m=262g\\
n=2mol\\\\
M_{r}=\frac{262g}{2mol}=131\frac{g}{mol}[/tex]
This element must be xenon.
