[By Lussac’s law]

2C_{6}H_{6} + 7O_{2} → 4CO_{2} + 6H_{2}O

2 vol : 7 vol → 4 vol : 6 vol

**To calculate the volume of unused oxygen.**

C_{6}H_{6 } : O_{2}

2 : 7

600 : x

⇒ x = 600 × 7\over 2

⇒ x = 2100 cc

Therefore, **volume of unused oxygen = 2500 – 2100 = 400 cc**

To calculate the volume of carbon dioxide formed

C_{6}H_{6 } : CO_{2}

2 : 4

600 : x

⇒ x = 600 × 4\over 2 = 1200 cc

Therefore, **volume of carbon dioxide formed is 1200 cc**