Question

The atomic number and mass number of sodium are $ 11 $ and $ 23 $ respectively. What information is conveyed by this statement?

Answer 1

Hint :The atomic number is the number of protons present in the chemical element. And the mass number is the total number of neutrons and protons in that chemical element.
 $ A = Z + N $
Where,
 $ A $ = Mass number of the element
 $ Z $ = Atomic number of the element
  $ N $ = Number of neutrons in the element.

Complete Step By Step Answer:
 As we know the number of electrons is equal to the number of protons present in that element that is the atomic number of that element.
For example:
Let $ Z $ be the atomic number of any element.
So, Number of electrons in that element will be: $ Z $
And also, Number of protons in that element will be: $ Z $
Mass number is the total number of protons and neutrons in the chemical element. So in simple words, we can state that mass number is the number of nucleons in the chemical element.
For example:
Let $ A $ be the mass number of any element.
And, $ Z $ be the Atomic number of elements.
And, $ N $ be the number of neutrons of the element.
So,
  $ A = Z + N $
Similarly,
From the above explanation we can conclude that,
The atomic number of sodium is $ 11 $ that means the number of protons in sodium is $ 11 $ and also the number of electrons in sodium is $ 11 $ .
And the mass number of sodium is $ 23 $ that means the total number of protons and neutrons in sodium is $ 23 $ .
As, $ A = Z + N $
 $ 23 = 11 + N $
 $ N = 23 - 11 $
 $ N = 12 $
That is, the number of neutrons in the sodium is $ 12 $ .

Note :
Each element in the periodic table has its own specific properties which totally depends on the number of electrons present in that element. Protons and neutrons together known as nucleons. Atomic number is also called proton number and mass number is also called atomic mass number.