Question

The mass number is the sum of the number of protons and the number of neutrons in an atom.
State whether the given statement is true or false.
A.True
B.False

Answer 1

Mass number is given by adding both the number of protons and neutrons whereas; the atomic number is the sum of the number of protons only.

Complete step by step answer:
The no of protons determines an element’s atomic no. and is used to distinguish one element from the other. Together, the no. of protons and the no. of neutrons determine an element’s mass number. So, the given statement that mass no. is the sum of the no. of neutrons and protons is correct.
It is true.

So, option-A is correct.
Additional Information:
Mass Number: Also known as atomic mass no. or nucleon no., it is the total no. of protons and neutrons in an atomic nucleus. It is approximately equal to the atomic mass of the atom expressed in atomic units. The symbol for mass no. is $\text{A}$ and it comes from the German word “Atomgewicht” meaning atomic weight. The mass no. is different for each different isotope of a chemical element.
Atomic no. is given by the no. of protons only and it is denoted by $\text{Z}$. so, the difference between the mass no. and the atomic no. $\text{Z}$ gives the no. of neutrons $\left( \text{N} \right)$ in a given nucleus as $\text{A = P + N}$ and $\text{Z = P}$ so, $\text{N = A}-\text{Z}$. The mass no. is written either after the element name or as a superscript to the left of an element’s symbol.
The periodic table trend for atomic mass is that it generally increases from left to right and always increases from top to bottom.
Isotopes: These are the variants of a particular chemical element which differ in neutron no., and consequently in mass no. An isotope of a given element has the same no. of protons but different no. of neutrons in each atom.

Note:
Proton is a subatomic particle with a positive electric charge of $+1e$ and mass slightly less than that of a neutron. Protons and neutrons each with masses of approximately one atomic mass unit, are collectively referred to as “nucleons”. The protons inside an atom’s nucleus help bind the nucleus together. The no. of protons in an atom’s nucleus determines which chemical element it is.