Question

How many moles of electrons weighs one kilogram?
[Mass of electron $=9.108\times {10}^{-31}kg$, Avogadro's number $=6.023\times {10}^{23}$].

• A. $6.023\times {10}^{23}$
• B. $\frac{1}{9.108}\times {10}^{31}$
• C. $\frac{6.023}{9.108}\times {10}^{54}$
• D. $\frac{1}{9.108\times 6.023}\times {10}^8$

Answer 1

The correct option is D $\frac{1}{9.108\times 6.023}\times {10}^8$

Total mass $=$ 1 kg

Mass of one electron $=9.108\times {10}^{-31}kg$

Number of electrons present in 1 kg of sample $=\frac{1kg}{9.108\times {10}^{-31}kg}=1.0979\times {10}^{30}$
Avogadro's number $=6.023\times {10}^{23}$

The number of moles of electrons weighs one kilogram

$=\frac{1}{9.108\times {10}^{-31}\times 6.023\times {10}^{23}}$

The number of moles of electrons weigh one kilogram $=\frac{1}{9.108\times 6.023}\times {10}^8$

Hence, the correct option is $D$