Question

how many electrons are present in 5 kg​

Answer 1

An electron is 1/1836 of the mass of a proton. So you take the atomic weight of the H1 isotope of hydrogen, which is 1. Then 1 kg of H1 hydrogen has 1,000 moles. Multiply by Avogadro’s number, 6.022140857 × 10^23. You get 6.022 x 10^26 atoms of hydrogen in a kilogram. Then you multiply by 1,836 because there are that many more times the number of electrons in a kilogram (you won’t be able to confine them though!) — so you have 1.10566 x 10^30 electrons in a kilogram of them. Nifty! That’s close to two tons of hydrogen — about your standard blimp. Actually there are other issues too, so you have to twiddle your pencil and do extra research if you want really exact figures.