The empirical formula of a compound is CH and its molecular mass is 78, its molecular formula is ______

Options

A. `C_2H_4`
B. `C_4H_8`
C. `C_6H_6`
D. `C_2H_2`

Explanation

To find the molecular formula of a compound when given its empirical formula and molecular mass, follow these steps:

### Step 1: Identify the empirical formula and its molecular mass
The empirical formula given is CH. The molecular mass of the compound is given as 78.

### Step 2: Calculate the molecular mass of the empirical formula
The empirical formula CH consists of:
- Carbon (C): 1 atom with a mass of approximately 12 g/mol
- Hydrogen (H): 1 atom with a mass of approximately 1 g/mol

Now, calculate the molecular mass of the empirical formula:
\[ \text{Molecular mass of CH} = \text{mass of C} + \text{mass of H} = 12 + 1 = 13 \text{ g/mol} \]

### Step 3: Determine the index (n)
To find the index (n), use the formula:
\[ n = \frac{\text{Molecular mass of the compound}}{\text{Molecular mass of the empirical formula}} \]
Substituting the values:
\[ n = \frac{78}{13} = 6 \]

### Step 4: Calculate the molecular formula
The molecular formula can be calculated by multiplying the empirical formula by the index (n):
\[ \text{Molecular formula} = n \times \text{Empirical formula} = 6 \times \text{CH} \]
This gives:
\[ \text{Molecular formula} = C_6H_6 \]

### Final Answer
The molecular formula of the compound is **C₆H₆**.

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