(A)14 elements in the sixth period (atomic no. = 90 to 103) that are filling the 4f-sublevel
(B)14 elements in the seventh period (atomic no. = 90 to 103) that are filling the 5f-sublevel
(C)14 elements in the sixth period (atomic no. = 58 to 71) that are filling the 4f-sublevelCorrect
(D)14 elements in the seventh period (atomic no. = 58 to 71) that are filling the 4f-sublevel
Answer: (C)
Solution
The lanthanoids are the 14 elements of the sixth period with atomic numbers 58 (Ce) to 71 (Lu), in which the 4f subshell is progressively filled. Option (a) has the wrong
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