Pure water vapour is trapped in a vessel of volume 10 ml. The relative humidity is 40%. The vapour i — States of Matter and Gaseous State Chemistry Question

💡 Solution & Explanation

Relative humidity $= P / P_{sat} = 0.40$. Initial pressure is $P_1 = 0.40 P_{sat}$. Condensation begins when the pressure reaches $P_{sat}$. Since temperature is constant, Boyle's law applies: $P_1 V_1 = P_2 V_2$. $(0.40 P_{sat})(10) = (P_{sat})(V_2)$. Solving for $V_2$ gives $V_2 = 4\text{ ml}$. Therefore, correct answer is 4.