Question

what is the electronic configuration of atomic number 19 and mass number 40?​

Answer 1

your answer is

2,8,8,1

The electronic configuration of the element with Atomic number 19 is 2,8,8,1 or  1s22s22p63s23p64s1 or [Ar]4s1. The element is potassium. It is an alkali metal with one valence electron.

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Answer 2

Explanation:

1s² 2s²2p⁶3s² 3p⁶4s¹

1s²2s²2p⁶3s²3p⁶[4s¹]=Argon[4s¹]