Question

The atom of an element is made up of $4$ protons, $5$ neutrons and $4$ electrons. What is its atomic number and mass number?

Answer 1

The atomic number is equal to the number of protons in an element whereas the mass number is equal to the sum of the number of protons and neutrons.

As per the given data:
Number of Protons $=4$
Number of neutrons $=5$
Number of electrons $=4$

So, mass number $=$ Number of Protons $+$ Number of neutrons $=4+5=9$

Hence, the atomic number of the given element is $4$, whereas mass number is $9$.