Question

Li, si, na, p, he. Which of not these elements belong to period 3? Explain

Answer 1

Explanation:

Li = Lithium

atomic number = 3

electronic configuration = 2 , 1

si = silicon

atomic number = 14

electronic configuration =2 , 8 , 4

Na = Sodium

atomic number = 11

electronic configuration 2, 8, 1

P = Phosphorus

atomic number = 15

electronic configuration = 2,8,5

He = Helium

atomic number =2

electronic configuration = 2

Since only Lithium and Helium have 2 shells so they belongs to 2nd period elements.

Silicon, Sodium and phosphorus have 3 shells so they belong to 3rd period elements.

Answer 2

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