Question

There are 201 equidistant rows of spectators sitting in a hall. A magician releases laughing gas, N2O (molwt = 44) from the front and the tear gas (molwt = 176) from the rear of the hall simultaneously. Which row of spectators will have a tendency to smile and weep simultaneously at first ?

• A. At 134th row if the numbering of rows start from front.
• B. At 67th row if the numbering of rows start from front.
• C. At 134th row if the numbering of rows start from the rear.
• D. At 113th row if the numbering of rows start from front.

Answer 1

Answer: (A)

At 134th row if the numbering of rows start from front.

Answer 2

Let at n^th row from the front both N₂O and tear gas meet simultaneously

\ $\frac{n}{201 - n}$ = $\frac{r_{N_{2}O}}{r_{tear}}$ $\sqrt{\frac{M_{tear}}{M_{N_{2}O}}}$=$\sqrt{\frac{176}{44}}$= 2

\ n = 2 × 201 – 2n

or 3n = 2 × 201

or n = $\frac{2 \times 201}{3}$= 134

\both gas first meet at 134^th row if numbering start from front.