1. Find the mass of carbon from $CO_2$ produced

From combustion, all carbon in the hydrocarbon becomes $CO_2$.

Given: $88\,\text{g of } CO_2$

Molar mass of $CO_2 = 44\,\text{g/mol}$, so $\text{moles of } CO_2 = \frac{88}{44} = 2$

Each mole of $CO_2$ contains $1$ mole of carbon, so moles of carbon = $2$.

Hence mass of carbon: $m_C = 2 \times 12 = 24\,\text{g}$

2. Find the mass of hydrogen from $H_2O$ produced

All hydrogen in the hydrocarbon becomes $H_2O$.

Given: $9\,\text{g of } H_2O$

Molar mass of $H_2O = 18\,\text{g/mol}$, so $\text{moles of } H_2O = \frac{9}{18} = 0.5$

Each mole of $H_2O$ contains $2$ moles of hydrogen atoms, so moles of hydrogen atoms: $0.5 \times 2 = 1$

Hence mass of hydrogen: $m_H = 1 \times 1 = 1\,\text{g}$

3. Check total mass

$m_C + m_H = 24 + 1 = 25\,\text{g}$

This matches the given mass of the hydrocarbon, so the composition is correct.

4. Compare with options

• A: $18$ g C and $7$ g H ❌
• B: $20$ g C and $5$ g H ❌
• C: $22$ g C and $3$ g H ❌
• D: $24$ g C and $1$ g H ✅

Therefore, the unknown hydrocarbon contains $24$ g of carbon and $1$ g of hydrogen.