A compound contains 20% sulphur. The molecular weight of the compound could be

Options

A. 80
B. 240
C. 400
D. 640

Answer

To determine the molecular weight of a compound that contains 20% sulfur, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Percentage Composition**:
The compound contains 20% sulfur by mass. This means that in 100 grams of the compound, there are 20 grams of sulfur.

2. **Identify the Atomic Mass of Sulfur**:
The atomic mass of sulfur (S) is approximately 32 g/mol.

3. **Set Up the Equation for Percentage Composition**:
The percentage of sulfur in the compound can be expressed as:
\[ \text{Percentage of Sulfur} = \left( \frac{\text{Mass of Sulfur in the compound}}{\text{Molecular Weight of the Compound}} \right) \times 100 \]
Plugging in the known values, we have:
\[ 20 = \left( \frac{32}{M} \right) \times 100 \]

4. **Rearrange the Equation**:
To find the molecular weight (M), rearrange the equation:
\[ 20M = 32 \times 100 \]
\[ 20M = 3200 \]
\[ M = \frac{3200}{20} \]
\[ M = 160 \text{ g/mol} \]

5. **Determine the Molecular Weight**:
The molecular weight of the compound must be an integral multiple of the empirical formula mass. Therefore, the molecular weight could be 160, 320, 480, 640, etc.

6. **Check the Options**:
If the options provided include 640, we can conclude that it is a valid molecular weight since it is a multiple of 160.

### Final Answer:
The molecular weight of the compound could be **640 g/mol**.

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