$20 \mathrm{~mL}$ of methane is completely burnt using $50 \mathrm{~mL}$ of oxygen. The volume of the gas left after cooling to room temperature is

• A

  $40 \mathrm{~mL}$
• B

  $60 \mathrm{~mL}$
• Correct answer
  C

  $30 \mathrm{~mL}$
• D

  $80 \mathrm{~mL}$

Solution

$\therefore$ Volume of gas left after cooling $=10 \mathrm{mLO}_{2}+20 \mathrm{~mL} \mathrm{CO}_{2}=30 \mathrm{~mL}$ $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ will be condense to $\mathrm{H}_{2} \mathrm{O}(\mathrm{l})$ after cooling.

Hence, the correct answer is option: 'C'.