Question

The number of molecules in 100 cc of gas at N.T.P. is ______ if the mass of each molecule is 4.556 x 10^-25 kg and R.M.S. speed is 250 m/s. 

Options

• 5.4 x 10¹⁹

• 1.05 x 10²¹

• 5.4 x 10¹⁸

• 1.05 x 10²⁰

Answer 1

1.05 x 10²¹

Explanation:

P = `1/3 "mn"/"V" "v"_"rms"^2`

∴ n = `(3"PV")/("mv"_"rms"^2) = (3 xx 10^5 xx 100 xx 10^-6)/(4.556 xx 10^-25 xx 250^2) ≈ 1.05 xx 10^21`