Question

Mass of one atom of an element is $2.66\times {10}^{-23}g$. This mass is equal to :

• A. $16amu$
• B. $2.39\times {10}^{-9}J$
• C. Both are correct
• D. None of these

Answer 1

The correct option is C Both are correct

1 amu = $1.67\times {10}^{-24}g$

So $2.66\times {10}^{-23}g$ in amu is calculated as :

$\frac{1}{1.67\times {10}^{-24}}\times 2.66\times {10}^{-23}=15.93amu$

Mass is converted to Joules by using Einstein's equation as :

$E=m\times c^2$ where c=speed of light = $3\times {10}^{8}m/s$ and mass in kg

Therefore for the given mass $E=2.66\times {10}^{-26}\times {(3\times {10}^8)}^2$

$E=2.39\times {10}^{-9}J$

Hence $2.66\times {10}^{-23}g=15.93(\approx 16)amu=2.39\times {10}^{-9}J$

Option C is correct.