Question

An element ‘X’ has a mass number 19 and contains 10 neutrons. What is the valency of ‘X’?

• A. 1
• B. 7
• C. 3
• D. 5

Answer 1

The correct option is A 1

We know that,
Mass Number = Number of protons + Number of neutrons
19 = p +10
p = 19 - 10 = 9
Since 'X' is a neutral atom,
Number of electrons(e) = number of protons (p) = 9
Therefore, the electronic configuration of 'X' is 2, 7. Here, L is the valence shell and there are seven electrons in valence shell.
Since the valency of an element is the number of electrons gained, lost, or shared to attain stable electronic configuration, the valency of 'X' is 1.