May/June 2026 Paper 23

Group 18 elements exist as colourless gases at room temperature and pressure.

Use Table 2.1 to describe and explain the variation in atomic radius down Group 18.

Identify one Group 18 element from Table 2.1 that behaves most like an ideal gas under standard conditions. Explain your answer.

A sample of $1.775\text{g}$ of gas X occupies $617.0{\text{cm}}^3$ at $300\text{K}$ and $101\text{kPa}$.

Calculate the relative molecular mass, $M_r$, of X assuming that X behaves as an ideal gas.