Question

10. The number of elements present in 2nd, 3rd 4th and 5th periods of modern periodic table respectively are
1) 2, 8, 8 & 18
2) 8, 8, 18 & 32
3) 8, 8, 18 & 18
4)8, 18, 18 & 32
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Answer 1

Answer:

(3)8,8,18,18

Explanation:

The answer is (3)8,8,18,18.

Answer 2

Answer:

The number of elements present in 2nd, 3rd 4th and 5th periods of modern periodic table respectively are 8, 8, 18 & 18.

Therefore, the option (3) is correct.

Explanation:

In modern periodic table:

• The number of elements present in second period are eight. The elements in which the filling of last electron in 2s orbital or 2p- orbital are present in 2nd period.
• Number of elements present in third period are eight. The elements in which the filling of last electron in 3s orbital or 3p- orbital are present in 3rd period.
• In fourth period, the number of elements present are 18. The elements in which the filling of last electron in 4s or 4p or 3d- orbital are present in 4th period.
• The number of elements present in fifth period are 18. The elements in which the filling of last electron in 5s or 5p or 4d-orbital are present in 5th period.