The elements in which electrons are progressively filled in 4f-orbital are called

(i) Actinoids

(ii) Transition elements

(iii) Lanthanoids

(iv) Halogens

Answers (1)

The answer is the option (iii) Lanthanoids

Explanation: The sixth period (n = 6) contains 32 elements, and after that, the successive electrons enter the 6s, 4f, 5d and 6p orbitals and in that order,  filling up of ff orbital begins with cerium (Z=58) and ends at Lutetium(Z=71). This complete 4f inner transition series is called the lanthanoid series.

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