Q. Lanthanides are
A) 14 elements in the sixth period (atomic no. = 90 to 103) that are filling $4f$sub level.
B) 14 elements in the seventh period (atomic no. = 90 to 103) that are filling $5f\$sub level.
C) 14 elements in the sixth period (atomic no. = 58 to 71) that are filling $4f\$sub-level.
D) 14 elements in the seventh period (atomic no. = 58 to 71) that are filling $4f\$sub-level.
Explanation
(c)
Lanthanides are the 14 elements of IIIB group and sixth period (At. no.=58 to 71) that are filling 4$f$-subshell of antipenultimate shell from 1 to 14 . Actually, they are placed below the Periodic Table in horizontal row as lanthanide series.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.