The correct option is A 10
′g′ subshell filling starts after the ′7p′ subshell is completely filled. That means s,p,d,f subshells of 4th and 5th shells are completely filled s,p,d subshell. 's' subshell of 8th shell is filled. The total number of electrons would be 120. The atomic number of the element with one electron in the 5g subshell is 121. If 111 is the last element, 10 more elements are to be discovered.111th element belongs to' block. There is a vacancy for one more element in' block 6 elements go to ′p′ block. 2 elements go to ′s′ block. The next element contains differentiating electron in the 5g subshell. It belongs to 8th period.