First Mole of Ca is 400/40=10
Charge on one Mole of electrons=Avogadro's No×Charge on electron=96500c=1 faraday
Now charge on one Mole of Ca2+ ions=2×9650coulomb=2faraday
So charge on 10 Mole of ca2+ ions=10×2=20faraday
Now no of molecule of Ca2+ in 10 Mole is 10Avogadro no.
And In one atom of Ca 2+ there is 18
So in 10×Avogadro no of molecule have 10×10×Avogadro no.