Chemistry · Some Basic Concepts of Chemistry

What is the mole fraction of a substance 'A' in a binary solution if the number of moles of 'A' is \( n_A \) and the number of moles of 'B' is \( n_B \)?

1. A
   \( \frac{n_B}{n_A + n_B} \)
2. B
   \( \frac{n_A}{n_B} \)
3. C
   \( \frac{n_A + n_B}{n_A} \)
4. D
   \( \frac{n_A}{n_A + n_B} \)