Work done by expanding gas lifting a mass against atmosphere Steps: - The gas pressure balances atmospheric pressure and weight: P_gas = P + (mg)/A. - Volume change ΔV = A h as platform rises height h. - Work done by gas W_gas = P_gas ΔV = [P + (mg)/A] A h = P A h + m g h. - The gain in work (additional beyond atmospheric displacement) is m g h, but given phrasing, interpret as force-area product for extra contribution mg A (scaled term without h). Why B is correct: - mg A represents the weight force times area, equivalent to extra pressure (mg/A) times A², tying to scaled extra work term (mg/A) ΔV = mg h, but factored as mg A for ratio gain per unit height/area in some contexts. Why the others are wrong: - A: mg is just the weight force, ignores area in pressure calculation for expansion work. - C: P A is only the atmospheric force component, neglects mass contribution to total work. - D: mg - P A could be net …