Question

A 100 feet long classroom maintains seating row after every 10 feet and has doors on both front and back sides. A laughing gas $\left(N_{2}O\right)$ cylinder and a tear gas (methane) cylinder were opened simultaneously at the front and the back door respectively. Assuming both the gases were present at the same temperature and pressure and the cylinder has similar valve dimensions. If the student of $n^{th}$ row, from the front, simultaneously weeps and laughs, the value of n is .

• A. 5
• B. 4
• C. 6
• D. 7

Answer 1

The correct option is B 4

$\therefore x=37.6ft$.

So, both the gases will first meet between $3^{rd}$ and $4^{th}$ row.
$\frac{d_{N_{2}O}}{d_{C{H}_4}}=\sqrt{\frac{16}{44}}=\frac{0.6}{1}$, therefore, while $N_{2}O$ travels 2.4 ft. to reach the $4^{th}$ row from the front, $C{H}_4$ would have travelled only 4 ft. towards the $3^{rd}$ row (so, it will not reach the $3^{rd}$ row by then). So, the student of $4^{th}$ row from the front will first weep and laugh simultaneously.