Because the charges on the electron and proton have the same absolute value, atoms are electrically neutral. Suppose this were not precisely true, and the absolute value of the charge of the electron were less than the charge of the proton by 0.00100%.
Estimate what the net charge of the textbook of mass about 1.0 kg would be under these circumstances. Make any assumptions you feel are justified. (Hint: Most of the atoms in this textbook have equal numbers of electrons, protons, and neutrons.)