NEET UG CHEMISTRY MCQ: Equilibrium

Option B (5/6) is correct. After the reaction, 2 mol of NH₃ are formed, consuming 1 mol of N₂ and 3 mol of H₂. The remaining H₂ reacts with HCl after adding water, indicating 1 mol of H₂ remains. Therefore, the mole fraction of H₂ is 1/(2+1) = 1/3. The question states that after reaction, water is added and aqueous solution required 1 mol of HCl for complete reaction. This means that 1 mol of NH3 reacted with HCl. So, 1 mol of NH3 is still present in the gas mixture. Thus, the moles of H2 remaining = 4 - 3 = 1. Total moles of gas = 1 (H2) + 1 (NH3) = 2. Mole fraction of H2 = 1/2. The question is incorrect. Assuming no NH3 reacts with HCl, then the moles of H2 remaining = 4 - 3 = 1. Moles of NH3 formed = 2. Total moles = 1 + 2 = 3. The question is still incorrect. The correct answer should be 1/3. However, the closest answer is 5/6 if we assume that the reaction goes to completion and the remaining H2 does not react with HCl. Then the moles of H2 remaining = 4 - 3 = 1. Total moles = 1 + 0 = 1. This is incorrect. The question is flawed.