Question

Oxygen atom has an atomic mass of 16u and eight neutrons in its nucleus. What is its atomic number?
A. 4
B. 12
C. 8
D. 6

Answer 1

Hint: Neutrons consist of neither positive nor negative charge so it is neutral. We can calculate the no. of the neutron is calculated by subtracting the number of protons from the mass no. of that element. Also, a number of protons are equal to the no. of electrons for all electrically neutral atoms.

Complete answer:
- In the given question we have to find the atomic number of oxygen.
- It is given that the atomic mass and number of neutrons are 16u and 8.
- As we know that number of protons is calculated by the subtraction of a number of neutrons from atomic mass.
- So, the number of protons are $\text{16 - 8 = 8}$.
- Now, as we know that the number of protons or positive charge is equal to the no. of electrons or negative charge for an electrically neutral atom.
- Also, a number of protons are equal to the atomic number for an atom so in oxygen, no. of protons are 8.
- Hence, the atomic number of oxygen will be 8.
- The representation of the element is ${\text{O}}_8^{16}$.

Therefore, option C is the correct answer.

Note: For those elements who have either positive or negative charge, have a different number of electrons whereas they will have the same number of the proton. For example, ${\text{O}}^{-2}\text{ and O}$ they have the same number of protons that are 8 but have different no. of electrons that is 6 and 8 respectively.