A one paisa coin is made up of aluminium and weighs $0.75 g.$ It has a square shape and its diagonal measures $17 mm.$ It is electrically neutral and contains equal amounts of positive and negative charges. The magnitude of these charges is (Atomic mass of $Al =26.98 g$)

Mass of the coin$= 0.75 g,$

Atomic mass of aluminium $=26.98 g$

Number of Al atoms in the coin,

$N=\frac{6.02\times {10}^{23}}{26.98}\times 0.75=1.67\times {10}^{22}$

As atomic number (Z) of Al is 13, each atom of Al contain 13 protons and 13 electrons. Magnitude of positive and negative charges in one paisa coin 

$=NZe=1.67\times {10}^{22}\times 13\times 1.6\times {10}^{-19}C=3.47\times {10}^{4}C$