If `10^(21)` molecules are removed from 200 mg of `CO_(2)`, the number of moles of `CO_(2)` left will be ?

Options

A. `2.85xx10^(-3)`
B. `28.8xx10^(-3)`
C. `0.288xx10^(-3)`
D. `1.68xx10^(-2)`

Answer

A

Explanation

200 mg of `CO_(2) = 200xx10^(-3)=0.2g`
`44`g of `CO_(2) ~~ 6xx10^(23)` molecules (approx)
0.2 g of `CO_(2)= (6xx10^(23))/44xx0.2=0.0272xx10^(23)`
`=2.72xx10^(21)` molecule
Now `10^(21)` molecule are removed.
So remaining molecules `=2.72xx10^(21)-10^(21)=10^(21) (2.72-1)=1.72xx10^(21)` molecules
Now, `6.023xx10^(23)` molecules = 1 mol
`1.72xx10^(21)` molecules `=(1xx1.72xx10^(21))/(6.023xx10^(23))=0.285xx10^(-2)`
`=2.85xx10^(-3)`.