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
(a) For n=1, maximum number of states = = 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.