JAMB Chemistry 2020 Paper

Concept:At constant volume and temperature, the pressure of a gas is directly proportional to the number of moles present.Explanation:From the ideal gas equation, $PV = nRT$.Since the container volume, $V$, and temperature, $T$, remain unchanged, pressure depends only on the amount of gas, $n$.If the quantity of oxygen is reduced by one-half, then $n_2 = \frac{n_1}{2}$.Thus, the pressure is also halved: $P_2 = \frac{P_1}{2}$.Substituting the given pressure, $P_2 = \frac{0.825\ \text{atm}}{2}$.$P_2 = 0.4125\ \text{atm} \approx 0.413\ \text{atm}$.Therefore, the remaining gas exerts a lower pressure, not a higher one, because the number of gas particles has decreased.Answer:C. 0.413 atm