JEE Main 2024 · 30 January · evening · Single correct · +4 / −1
If a substance 'A' dissolves in solution of a mixture of 'B' and 'C' with their respective number of moles as n_A, n_B and n_(C₃). Mole fraction of C in the solution is
- (a) n_C/(n_A × n_B × n_C)
- (b) n_B/(n_A+n_B)
- (c) n_C/(n_A+n_B+n_C)
- (d) n_C/(n_A-n_B-n_C)
Answer and solution
Answer (c) n_C/(n_A+n_B+n_C)
Solution
Chemistry ma’am · 3 steps
Mole fraction is always a part over the whole, and the whole means every component, A included.
- Definition. The mole fraction of a component is its moles divided by the total moles of all components in the solution.
- Count every component. This solution contains three substances: A, B and C. So the total number of moles is n_A + n_B + n_C.
x_C = n_C/(n_A + n_B + n_C)
- So. The mole fraction of C is n_C/(n_A + n_B + n_C), which is option (c).
The idea to keep. For any component, mole fraction = its moles divided by the sum of moles of everything present. All the mole fractions in a solution add up to 1.
Answer from the NTA final answer key. Solution by PrepWiser.