Question

What does the mass number of an atom represent?
A.Only the number of protons
B.The number of protons and neutrons
C.The number of protons and electrons
D.Only the number of neutrons

Answer 1

Hint: The mass number for carbon is 12 but its atomic number is 6. The mass number of an atom is different from the atomic number of the atom.

Complete answer step by step:
-Each element has its own mass number and atomic number.
-These two numbers are fixed for the particular element.
-The atomic number is the number of protons or electrons found in the element and it is going to be denoted with Z.
Atomic number = number of protons or electrons present
-The mass number is nothing but the sum of nucleons (protons and neutrons) in the nucleus of an element.
Mass number = number protons + number of neutrons

So, option B is correct.

Additional information:
-The elements arranged in the modern periodic table in such a way that all the elements have an increasing atomic number vice versa increasing mass number.
-The neutral elements contain an equal number of protons and electrons.
-In isotopes the number of neutrons is variable.
-The isotopes have somewhat different mass numbers.
-The atomic mass is calculated by obtaining the mean of the mass numbers for its isotopes.

Note: Don’t be confused with the words electron and neutron and proton.
An electron is a negatively charged particle that revolves around the nucleus in a particular orbit.
Proton is a positively charged particle located in the nucleus of an atom.
Neutron is a particle having no charge and located in the nucleus.