Concept:The mass number of a nucleus is the total count of its heavy particles: protons and neutrons.
Explanation:Inside the nucleus, protons and neutrons together are called nucleons.
The mass number is simply the sum of these nucleons.
It is represented by the letter
A.
For an atom,
A=Z+N, where
Z is the number of protons and
N is the number of neutrons.
This sum is usually a whole number and is not a fraction.
It can be more or less than the atomic weight depending on isotopes, so option C is not always true.
It is always greater than or equal to the atomic number, never less, so option A is false.
Therefore, the correct definition is the sum of protons and neutrons.
Answer:B. The sum of the number of protons and neutrons present in the nucleus.