(a) What is the main characteristic of the last elements in the periods of the periodic table? What is the general name of such elements?

(b) What is the number of elements in (a) 1st period, and (b) 3rd period, of the modern periodic table?

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Solution

(a) The last elements in the periods of the periodic table have their valence shells completely filled with electrons. They are known as noble or inert gases. Their valency is zero.

(b) The number of elements in (a) 1st period is 2 and (b) 3rd period is 8 in the modern periodic table.

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