Question

How many ${}^{12}\text{C}$ atoms are there in $24\text{mg}$ of ${}^{12}\text{C}$?

• A. $1.204\times {10}^{21}$
• B. $6.024\times {10}^{20}$
• C. $1.204\times {10}^{20}$
• D. $6.024\times {10}^{21}$

Answer 1

The correct option is A $1.204\times {10}^{21}$

We know, Atomic mass of ${}^{12}\text{C}=12\times 1.66\times {10}^{-24}\text{g}$
$=1.992\times {10}^{-23}\text{g}$
Therefore, mass of one atom of ${}^{12}\text{C}=1.992\times {10}^{-23}\text{g}$
Oppositely $1.992\times {10}^{-23}\text{g}$ of ${}^{12}\text{C}$ contain 1 atom of ${}^{12}\text{C}$
So, $0.024\text{g}$ of ${}^{12}\text{C}$ will contain $=\frac{0.024}{1.992\times {10}^{-23}}\text{C-atoms}$
$=1.204\times {10}^{21}\text{C atoms}$