A metal (mass number = 40) having same number of protons and neutrons,

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structureofatom

#1

A metal (mass number = 40) having same number of protons and neutrons, combines with two chlorine atoms. Identify the element with which electronic configuration of this metal matches in combined state.


#2

Mass number = Number of protons + number of neutrons
=> 40=2 x number of protons
=> Number of protons = 20 Hence, the metal is calcium (Ca).
Since, it combines with 2 Cl-atoms (total valency = 2)
Hence, it will acquire 2 positive charge, after losing 2 electrons as
Electronic configuration of ${{Ca}^{2+}}$ ion= 2, 8, 8(K,L,M)
This electronic configuration matches to that of argon (Ar).