Q.
$2.8\times10^{-3}$ mol of $\mathrm{CO_2}$ is left after removing $10^{21}$ molecules from its ' $x$ ' mg sample. The mass of $\mathrm{CO_2}$ taken initially is Given: $N_A=6.02\times10^{23}\ \mathrm{mol^{-1}}$
A) 98.3 mg
B) 48.2 mg
C) 196.2 mg
D) 150.4 mg
Explanation
[Solution by Dr. Abubacker] Moles removed $=\frac{10^{21}}{6.02\times10^{23}}=1.661\times10^{-3}$ mol. Initial moles $=2.8\times10^{-3}+1.661\times10^{-3}=4.461\times10^{-3}$ mol. Mass $=4.461\times10^{-3}\times44=196.3\approx196.2$ mg. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.