If in nature there may not be an element for which the principal quantum number n > 4, then the total possible number of elements will be

60 32 4 64

60

For n = 1, maximum number of states = 2n2 = 2 and for n = 2, 3, 4, maximum number of states would be 8, 18, 32 respectively. Hence number of possible elements = 2 + 8 + 18 + 32 = 60.