Which one of the following pair of compounds illustrate the law of multiple proportion

Options

A. `CuO and Cu_2O`
B. `SnCl_2` and `PbCl_2`
C. `CaC_2` and `CaSO_4`
D. `H_2O` and `D_2O`

Answer

To determine which pair of compounds illustrates the law of multiple proportions, we will follow these steps:

### Step 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 are in a ratio of small whole numbers.

### Step 2: Identify Compounds
We need to analyze the given pairs of compounds to see if they fit the law of multiple proportions. The compounds we are considering are:
1. Water (H2O) and Hydrogen Peroxide (H2O2)
2. Copper(I) oxide (Cu2O) and Copper(II) oxide (CuO)

### Step 3: Calculate the Masses of Elements
1. **For Water (H2O)**:
- Mass of Oxygen = 16 g (1 atom of O)
- Mass of Hydrogen = 2 g (2 atoms of H)

2. **For Hydrogen Peroxide (H2O2)**:
- Mass of Oxygen = 32 g (2 atoms of O)
- Mass of Hydrogen = 2 g (2 atoms of H)

Ratio of Oxygen in H2O to H2O2:
- 16 g (H2O) : 32 g (H2O2) = 1 : 2

3. **For Copper(I) oxide (Cu2O)**:
- Oxidation state of Copper = +1
- Mass of Copper = 2 * 63.5 g = 127 g (2 atoms of Cu)
- Mass of Oxygen = 16 g (1 atom of O)

4. **For Copper(II) oxide (CuO)**:
- Oxidation state of Copper = +2
- Mass of Copper = 63.5 g (1 atom of Cu)
- Mass of Oxygen = 16 g (1 atom of O)

Ratio of Copper in Cu2O to CuO:
- 127 g (Cu2O) : 63.5 g (CuO) does not yield a simple whole number ratio.

### Step 4: Conclusion
The pair of compounds that illustrates the law of multiple proportions is Water (H2O) and Hydrogen Peroxide (H2O2) because the ratio of the masses of oxygen in these two compounds (1:2) is a simple whole number ratio.

### Final Answer
The correct answer is the pair of compounds: **Water (H2O) and Hydrogen Peroxide (H2O2)**.

---