What is maximum number of electrons that can be present in an atom in which the highest principal quantum number is 4 ?......Please explain

@ jeeva 
formula for finding the maximum no of electron from the principal quantum no = 2 n square 
so, the total no of electron = 2 * (4 ) square = 32 
acc to the pauli exclusion principle there are twoi electron in each orbital with sign +1/2 and -1/.2 
so, the max no of electron here will be 32 and as far as no of electron with +1/2 are concerned then it will be 16 . 
HOPE IT CLEARS 
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