(a) As element X has mass number 40 and contains 21 neutrons in its atom. To which group of the periodic table does it belong?
(b) The element X forms a compound X2Y. Suggest an element that Y might be and give reasons for your choice.


(a) The element X belongs to Group 1 as its electronic configuration is 2, 8, 8, 1.
As Atomic number = Mass number - Number of Neutrons.
Atomic number = 40-21 =19.
Hence, its electronic configuration is 2,8,8,1.

(b) The element Y can be Oxygen because X is a monovalent element so Y has to be divalent to form the compound X2Y and oxygen has the valency of 2.

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Updated on: 10-Oct-2022

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