NDA General Ability Question (2025) — Solution

Step-by-step solution

At STP, 1 mole of any ideal gas occupies 22.4 litres. Half mole of nitrogen gas occupies 1 2 22.4 = 11.2 litres. This statement is correct. Molar mass of ammonia (NH_3) is 17 g/mol. 17 g of ammonia corresponds to 1 mole, which contains 6.022 10^ 23 molecules. This statement is correct. 22.4 litres of CO_2 gas at STP corresponds to 1 mole. The molar mass of CO_2 is 44 g/mol, so it weighs 44 grams. This statement is correct. Molar mass of hydrogen gas (H_2) is 2 g/mol. 4 grams of hydrogen gas corresponds to 4 2 = 2 moles. The number of molecules in 2 moles is 2 6.022 10^ 23 = 1.2044 10^ 24 molecules. This statement is incorrect. Answer: 4 gram of hydrogen gas contains 6.022 10^ 23 molecules