Question

A teacher enters a classroom from front door while a student from back door. There are 13 equidistant rows of benches in the classroom. The teacher releases N2O, the laughing gas, from the first bench while the student releases the weeping gas (C6H11OBr) from the last bench. At which row will the students starts laughing and weeping simultaneously

• A. 7
• B. 10
• C. 9
• D. 8

Answer 1

Answer: (C)

9

Answer 2

Let both gases meet at nth row

$\frac{r_{NO_{2}}}{r_{C_{6}H_{10}Br}} = \frac{x}{12 - x} = \sqrt{\frac{179}{44}} = 2$

x = 24 – 2x

3x = 24

x = 8 = n – 1

n = 9th Row