Question

Which was the incomplete period in the long-form of the modern periodic table?

(a) 7^th period

(b) 4^th period

(c) 6^th period

(d) 2^nd period

The question was posed to me during a job interview.

My question comes from Modern Periodic Law and the Present Form of the Periodic Table in chapter Classification of Elements and Periodicity in Properties of Chemistry – Class 11

Answer 1

The correct answer is (a) 7^th period

For explanation: The 7^th period follows the rule that the elements fill their 7s subshell first and then 5f, 6d and 7p (Plutonium is the exception). As the elements weren’t discovered completely, it was called the incomplete period.