Periodic Classification and Periodic Properties 2 Question 1
1. The group number, number of valence electrons and valency of an element with atomic number 15 , respectively, are
(2019 Main, 12 April I)
(a) 16,5 and 2
(b) 15,5 and 3
(c) 16,6 and 3
(d) 15,6 and 2
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Answer:
Correct Answer: 1. (b)
Solution:
- The group number, number of valence electrons and valency of an element with atomic number 15 are 15, 5 and 3 respectively. Modern periodic table is based on the atomic number. Number of valence electrons present in an atom decides the group number. Electronic configuration of element having atomic number $15=1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{3}$
$$ \text { Valence electrons } $$
As five electrons are present in valence shell, its group number is 15. Valency of element having atomic number 15 is +3 $(8-5=3)$.
