An unknown representative element has an atomic number . What is the principal quantum number (period number) of the element placed exactly below it in the same group of the modern periodic table?

Question

An unknown representative element $X$ has an atomic number $Z = 34$. What is the principal quantum number (period number) of the element placed exactly below it in the same group of the modern periodic table?

Prashant Kotian · Accepted Answer

Correct answer: 5. The element with is Selenium (), which has the configuration . Since the highest principal quantum number is , it belongs to the 4th period. The element placed exactly below it in Group 16 is Tellurium (), which naturally belongs to the 5th period.

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