You have collected (a) 2 litres of CO₂ (b) 3 litres of chlorine (c) 5 litres of hydrogen (d) 4 litres of nitrogen and (e) 1 litres of SO₂, under similar conditions of temperature and pressure. Which gas sample will have:

(a) the greatest number of molecules, and

(b) the least number of molecules?

Justify your answers.

According to Avogadro's law, equal volumes of all gases under similar conditions of temperature and pressure contain same number of molecules. So, under the same conditions of temperature and pressure, if volume of gas is decreased the number of molecules will also decrease.

Hence,

(a) 5 litres of hydrogen contain the greatest number of molecules as it has the highest volume.

(b) 1 litre of SO₂ contains the least number of molecules since it has the smallest volume.