Read the passage carefully and answer the Questions.
A homogeneous mixture of two or more than two components has uniform composition and properties. The binary solutions have two components, which may be solid, liquid or gas. The resultant solution has a larger amount of solvent and a smaller amount of solute. The amount of solute in a given amount of solvent decides the concentration of the resulting solution. The concentration can be expressed in various ways, like molarity, molality, normality and mole fraction.
Parts per million (ppm) is represented as
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(\text{parts per million}=\frac{\text{Number of parts of the component}}{\text{Total number of parts of all components of the solution}}\times10^6\)
When a solute is present in trace quantities, its fraction is a very small number, so it is multiplied by a large factor to give a convenient value. The fraction of the component (by mass, by volume or in moles) is the same in each case; only the factor changes:
fraction × 100 = percentage (parts per hundred)
fraction × 106 = parts per million (ppm)
For example, sea water containing 5.8 g of dissolved oxygen in 106 g has 5.8 ppm of oxygen.
Why the other options are incorrect
Option (2) \(\text{parts per million}=\frac{\text{Number of parts of the component}}{\text{Total number of parts of all components of the solution}}\times10^5\) — Incorrect. Multiplying by 105 gives parts per hundred thousand, not per million.
Option (3) \(\text{parts per million}=\frac{\text{Number of parts of the component}}{\text{Total number of parts of all components of the solution}}\times10^3\) — Incorrect. Multiplying by 103 gives parts per thousand.
Option (4) \(\text{parts per million}=\frac{\text{Total number of parts of all components of the solution}}{\text{Number of parts of the component}}\times10^6\) — Incorrect. The fraction is inverted: the component must be in the numerator, since ppm tells how many parts of the component are present in a million parts of the solution.
NCERT (2026-27 edition):
Parts per Million
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 03-06 S2 02-06 S1 29-05 S1 | – | – | – |