Question

find the no. of electrons in 20 microcoulombs

Answer 1

A single electron is 2×10^−19 C, so to make 2×10^−5 C you need about 10^14 electrons, or a hundred trillion. So give or take a few factors of ten, this is the number of electrons transferred from the hair to the brush. It's much more than a billion, but much much less than Avogadro's number.

Answer 2

Q=ne
n=q/e
q=20 micro coulombs
n=20*10 power -6 / 1.6 *10 power -19
12.5*10 power 13