How many moles of electrons weigh in one kilogram?

Mass of one electron is $9.108\times {10}^{-31} \mathrm{kg}$ and the number of electrons present in one mole is $6.023\times {10}^{23} \mathrm{electrons}.$

Mass of one mole of electrons determined by multiplying the number of electrons in one mole with the mass of one electron.

$\begin{array}{ccc}\mathrm{Mass} \mathrm{of} \mathrm{one} \mathrm{mole} \mathrm{of} \mathrm{electron}& =& 6.023\times {10}^{23}\times 9.108\times {10}^{-31}\\ & =& 6.023\times 9.108\times {10}^{-8} \mathrm{kg}\end{array}$

In the given problem, the total mass of electron is 1 kg and the mass of one mole of electron is $6.023\times 9.1\times {10}^{-8} \mathrm{kg}.$ Hence, the total number of moles of electron present in one kg is determined as:

$\mathrm{Number} \mathrm{of} \mathrm{moles} \mathrm{of} \mathrm{electrons} \mathrm{in} \mathrm{one} \mathrm{kg}=\frac{{10}^8}{9.108\times 6.023}$