Question

The mole fraction of the solute in a $1$ molal aqueous solution is:

• A. $1$
• B. $1.8$
• C. $18$
• D. $0.018$

Answer 1

The correct option is D $0.018$

1 molal aqueous solution means 1 mole of solute in 1 kg (or 1000 g) of water.
The molecular weight of water is 18 g/mol.

The number of moles of water $=\frac{1000g}{18g/mol}=55.56mol$

The mole fraction of the solute $=\frac{1mol}{1mol+55.56mol}=0.018$

Thus, option $D$ is correct.