A gas is found to have molecular formula `(CO)_(x)` . Its
vapour density is 70, the value of x must be:-

Options

A. 7
B. 4
C. 5
D. 6

Explanation

To solve the problem, we need to find the value of \( x \) in the molecular formula \( (CO)_{x} \) given that the vapor density of the gas is 70.

### Step-by-Step Solution:

1. **Understand the Relationship Between Vapor Density and Molecular Weight**:
The molecular weight (MW) of a gas is related to its vapor density (VD) by the formula:
\[ \text{Molecular Weight} = 2 \times \text{Vapor Density} \]

2. **Calculate the Molecular Weight**:
Given that the vapor density (VD) is 70, we can calculate the molecular weight (MW):
\[ \text{Molecular Weight} = 2 \times 70 = 140 \]

3. **Express the Molecular Weight in Terms of x**:
The molecular formula of the gas is \( (CO)_{x} \). The molecular weight can be calculated as:
- The atomic weight of Carbon (C) = 12 g/mol
- The atomic weight of Oxygen (O) = 16 g/mol
Therefore, the molecular weight of \( (CO)_{x} \) is:
\[ \text{Molecular Weight} = 12 + 16x \]

4. **Set Up the Equation**:
Now, we can set the expression for molecular weight equal to the calculated molecular weight:
\[ 12 + 16x = 140 \]

5. **Solve for x**:
Rearranging the equation to solve for \( x \):
\[ 16x = 140 - 12 \]
\[ 16x = 128 \]
\[ x = \frac{128}{16} = 8 \]

6. **Conclusion**:
The value of \( x \) must be 8. Therefore, the molecular formula of the gas is \( CO_8 \).

### Final Answer:
The value of \( x \) is 8.

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