The law of multiple proportion is illustrated by the two compounds :

Options

A. Sodium chlordie and sodium bromide
B. Ordinary water and heavy water
C. Caustic soda caustic potash
D. Sulphur dioxide and sulphur trixoide

Answer

To solve the question regarding the law of multiple proportions illustrated by two compounds, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Law of Multiple Proportions**:
The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element can be expressed in a ratio of small whole numbers.

2. **Identify the Compounds**:
We have four pairs of compounds to analyze:
- Sodium chloride (NaCl) and sodium bromide (NaBr)
- Ordinary water (H2O) and heavy water (D2O)
- Caustic soda (NaOH) and caustic potash (KOH)
- Sulfur dioxide (SO2) and sulfur trioxide (SO3)

3. **Analyze Each Pair**:
- **Sodium Chloride and Sodium Bromide**:
- NaCl and NaBr contain sodium (Na) combined with different halogens (Cl and Br). Since they involve different elements, they do not illustrate the law of multiple proportions.

- **Ordinary Water and Heavy Water**:
- H2O and D2O contain hydrogen (H) and deuterium (D), which are isotopes of hydrogen. While they are different forms of the same element, they do not fit the law of multiple proportions since the mass ratios do not represent a simple whole number ratio.

- **Caustic Soda and Caustic Potash**:
- NaOH and KOH contain sodium (Na) and potassium (K), which are different elements. Therefore, they do not illustrate the law of multiple proportions.

- **Sulfur Dioxide and Sulfur Trioxide**:
- SO2 and SO3 both contain sulfur (S) and oxygen (O). The mass of sulfur is fixed, and the mass of oxygen in SO2 is 32 g (2 × 16 g) and in SO3 is 48 g (3 × 16 g). The ratio of the masses of oxygen that combine with the same mass of sulfur (16 g) is 32:48, which simplifies to 2:3. This fits the law of multiple proportions.

4. **Conclusion**:
The pair of compounds that illustrates the law of multiple proportions is **Sulfur Dioxide (SO2) and Sulfur Trioxide (SO3)**.

### Final Answer:
The correct option is **D: Sulfur Dioxide (SO2) and Sulfur Trioxide (SO3)**.

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