The ground state electronic configuration of an element is . What is the atomic number of the element that is placed exactly below this element in the same group of the periodic table?

Question

The ground state electronic configuration of an element is $1s^2 2s^2 2p^6 3s^2 3p^3$. What is the atomic number of the element that is placed exactly below this element in the same group of the periodic table?

Prashant Kotian · Accepted Answer

Correct answer: C. The given configuration represents Phosphorus () with atomic number , which belongs to the 3rd period and 15th group (Nitrogen family). The element just below it belongs to the 4th period of the same group. Adding the magic number 18 (number of elements in the 4th period up to that group) to 15 gives , which is Arsenic ().

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