Question

From $320mg$ of $O_2,6.023\times {10}^{20}$ molecules are removed, the no. of moles remained are:

• A. $9\times {10}^{-3}$ moles
• B. $9\times {10}^{-2}$ moles
• C. $zero$
• D. $3\times {10}^{-3}$ moles

Answer 1

The correct option is A $9\times {10}^{-3}$ moles

$32g$ of $O_2=1mol=6.023\times {10}^{23}$ molecules

$\therefore 320mg=0.32g=0.01mol=6.023\times {10}^{21}$

From this $6.023\times {10}^{20}$ moles are removed= $0.001$ moles

$\therefore$ Remaining= $0.01-0.001=0.009$ moles

$=9\times {10}^{-3}$ moles .