Question

The number of carbon atoms present in a signature, if a signature written by carbon pencil weights $1.2\times {10}^{-3}$ g is:

• A. $12.04\times {10}^{20}$
• B. $6.02\times {10}^{19}$
• C. $3.01\times {10}^{19}$
• D. $6.02\times {10}^{20}$

Answer 1

The correct option is B

$6.02\times {10}^{19}$

Atomic weight of Carbon = 12 gm.

12 gm have Avagadro number of carbon atoms [$N_A$].

No. of carbon atoms in $1.2\times {10}^{-3}$ g = $\left(\frac{1.2\times {10}^{-3}}{12}\right)\times N_A=6.02\times {10}^{19}$. [$\because N_A=6.023\times {10}^{23}$]