JEE Chemistry 2024 Question with Solution

Given: The number of moles of substances are $n_a$, $n_b$, and $n_c$.

Find: The mole fraction of C in the solution.

The mole fraction of a component is defined as the ratio of the number of moles of that component to the total number of moles present in the solution.

So, the total number of moles is

$$n_a + n_b + n_c$$

Therefore, the mole fraction of C is

$$X_C = \frac{n_c}{n_a + n_b + n_c}$$

Thus, the correct expression is $\frac{n_c}{n_a + n_b + n_c}$. The solution states that the correct option is A. Since the listed options are only placeholders, the actual expression is not visible in the option text.

Given: Substance A dissolves in a mixture containing B and C, with moles $n_a$, $n_b$, and $n_c$.

Find: The mole fraction of component C.

By definition,

$$\text{Mole fraction of a component} = \frac{\text{moles of that component}}{\text{total moles of all components}}$$

Here, component C has $n_c$ moles, and the total moles in the solution are

$$n_a + n_b + n_c$$

Substituting into the definition,

$$X_C = \frac{n_c}{n_a + n_b + n_c}$$

Therefore, the mole fraction of C in the solution is $\frac{n_c}{n_a + n_b + n_c}$, corresponding to option A according to the solution.