Question

Atomic number of N is 7 and of oxygen is 8. The total number of electrons is $NO_3^ - $ ion is:
A. 32
B. 24
C. 33
D.35

Answer 1

Hint: The total number of electrons is the sum total of all the bonding pairs of electrons and nonbonding pairs of electrons (lone pairs) present in each atom which share their valence electrons with each other forms the molecule.

Complete step by step answer:
The atomic number of nitrogen is 7. The electronic configuration of nitrogen is $[He]2{s^2}2{p^3}$.
The atomic number of oxygen is 8. The electronic configuration of oxygen is $[He]2{s^2}2{p^4}$.
The number of electrons in nitrogen is 7.
The number of electrons in oxygen is 8.
The formula of nitrate ion is $NO_3^ - $. In nitrate ion one nitrogen atom and three oxygen atoms are present.
The negative charge on the ion shows that the molecule has gained electrons.
To calculate the total number of electrons present in nitrate ions, following steps are required.
STEP 1:
Multiply the number of atoms with the number of electrons present in the atom.
STEP 2:
Add the total electrons of an atom with the charge to find the total electrons in the ion or molecule.
The formula for the calculation of the total number of electrons in nitrate ions is shown below.
$ = (1 \times N\;{e^ - }) + (3 \times O\;{e^ - }) + 1$
To calculate the total number of electrons, substitute the values in the above expression.
$ = (1 \times 7) + (3 \times 8) + 1$
$ = 32$
Thus, the total number of electrons present in the nitrate ion is 32.
Therefore, the correct option is A.


Note:
The positive charge on the molecule or atom shows the loss of electrons by the respective molecule or atom and while calculating the total electrons of the ion the number of electrons is deducted.