Question

5. 48 dm3 of a gas has a mass of 262 grams. How many moles is this? What is the Mr? What must this element be?

Answer 1

0,262kg/0,00548 m³ = 47,8 kg/m³
Radon is the most dense elemental gas with a density of 9,73 kg/m³
so it's not an elemental gas.