Match the List-I with List-II.
| List-I | List-II |
| Concentration terms | Units |
| (A) Molarity | (I) mol kg−1 |
| (B) Mole Fraction | (II) mol L−1 |
| (C) Mole | (III) unitless |
| (D) Molality | (IV) mol |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) - (II), (B) - (III), (C) - (IV), (D) - (I)
The unit of each concentration term follows directly from its definition: divide the unit of the numerator by the unit of the denominator.
(A) Molarity — This matches (II) mol L−1. Molarity is the number of moles of solute per litre of solution.
\( \displaystyle M=\frac{\text{moles of solute}}{\text{volume of solution in L}}\ \Rightarrow\ \frac{\mathrm{mol}}{\mathrm{L}}=\mathrm{mol\,L^{-1}} \)
(B) Mole Fraction — This matches (III) unitless. It is a ratio of moles to moles, so the units cancel.
\( \displaystyle x_A=\frac{n_A}{n_A+n_B}\ \Rightarrow\ \frac{\mathrm{mol}}{\mathrm{mol}}=\text{no unit} \)
(C) Mole — This matches (IV) mol. The mole is itself the SI unit of amount of substance.
(D) Molality — This matches (I) mol kg−1. Molality is the number of moles of solute per kilogram of solvent.
\( \displaystyle m=\frac{\text{moles of solute}}{\text{mass of solvent in kg}}\ \Rightarrow\ \frac{\mathrm{mol}}{\mathrm{kg}}=\mathrm{mol\,kg^{-1}} \)
Shortcut: The pair (A)–(II) appears only in Option (2).