Which of the following is correct ?

Options

A. For a binary solution sum of the mole fractions of all components is equal to one
B. `("Mole fraction of I")/("Mole fraction of II")=("moles of I")/("moles of II")` (for binary solution)
C. Mole fraction of solute `=("moles of solute")/("moles of solute + moles of solvent")`
D. All

Explanation

To solve the question "Which of the following is correct?" regarding the properties of solutions, we will analyze each option step by step.

### Step-by-Step Solution:

**Step 1: Understanding Mole Fractions**
- In a binary solution consisting of components A and B, the mole fraction (X) of each component is defined as:
\[ X_A = \frac{n_A}{n_A + n_B} \quad \text{and} \quad X_B = \frac{n_B}{n_A + n_B} \]
- The sum of the mole fractions of all components in a solution must equal 1:
\[ X_A + X_B = \frac{n_A}{n_A + n_B} + \frac{n_B}{n_A + n_B} = \frac{n_A + n_B}{n_A + n_B} = 1 \]
- **Conclusion**: Option 1 is correct.

**Step 2: Relationship Between Mole Fractions**
- The relationship between the mole fractions of two components can be expressed as:
\[ \frac{X_A}{X_B} = \frac{n_A}{n_B} \]
- This can be derived from the definitions of mole fractions:
\[ \frac{X_A}{X_B} = \frac{\frac{n_A}{n_A + n_B}}{\frac{n_B}{n_A + n_B}} = \frac{n_A}{n_B} \]
- **Conclusion**: Option 2 is correct.

**Step 3: Mole Fraction of Solute**
- The mole fraction of the solute (let's consider A as the solute) is given by:
\[ X_A = \frac{n_A}{n_A + n_B} \]
- Here, \(n_A\) represents the moles of the solute, and \(n_B\) represents the moles of the solvent. Therefore, the expression for the mole fraction of the solute is indeed:
\[ X_A = \frac{\text{moles of solute}}{\text{moles of solute} + \text{moles of solvent}} \]
- **Conclusion**: Option 3 is correct.

### Final Conclusion:
Since all three options are correct, the answer to the question is that options 1, 2, and 3 are all correct.

---