( A ) 14 elements in the sixth period (atomic no. nt 90 to 103) that are filling 4f sublevel
( B ) 14 elements in the seventh period (atomic no. = 58 to 71) that are filling 4f sublevel
( C ) 14 elements in the sixth period (atomic no. 57 to 71) that are filling 4f sublevel
( D ) 14 elements in the seventh period (atomic no. = 90 to 103) that are filling 5f sublevel.
