An element X has mass number 40 and contains 21 neutrons in its atom. To which group of the Periodic Table does it belong?
- Group 1
- Group 4
- Group 2
- Group 3
Correct Answer: (a) Group 1
Explanation: The mass number of element X is 40 and the number of neutrons in its atom is 21.
We know, Atomic Number = Mass number- Number of neutrons = 40-21=19. Hence, the number of electrons is 19. Therefore, its electronic configuration is 2,8,8,1. Thus, element X belongs to group 1 as it has 1 valence electron.
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