Two gases $\mathrm{A}$ and $\mathrm{B}$ are released from the two ends of a tunnel of length $100 \mathrm{m}$. A travels $40 \min$, before meeting the gas $\mathrm{B}$ in the tunnel. If the molecular weight of $\mathrm{B}$ is $18$ , what is the molecular weight of $\mathrm{A}$ ?

• A

  $28.5$
• B

  $10.5$
• C

  $8.5$
• Correct answer
  D

  $40.5$

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