Question

Assertion: The mass number of hydrogen is equal to its atomic number.
Reason: H-atom has no neutrons.
a. Both assertion and reason are correct and reason is the correct explanation for assertion.
b. Both assertion and reason are correct but reason is not the correct explanation for assertion.
c. Assertion is correct but reason is incorrect
d. Assertion is correct but reason is incorrect.

Answer 1

Hint: We know that atomic number is the number of protons present in the nucleus and mass number is the sum of the number of protons and neutrons in the nucleus of an atom.

Complete step by step answer:
Atomic number is defined as the number of protons present in the nucleus of an atom. It is denoted by the letter ‘Z’.
Mass number is the sum of the number of protons and neutrons present in the nucleus of an atom. It is denoted by the letter ‘A’.
Hydrogen is the first element in the periodic table with the atomic number 1. This means that it has one proton in its nucleus. Also, hydrogen atoms do not contain any neutron. So, its mass number is equal to the number of protons only which is 1.
Hence, atomic number and mass number of hydrogen atom are both 1.
So, option A is correct.

Note: Since there are no neutrons present, atomic number = atomic mass number. Hence, the atomic number and mass number of hydrogen are 1. Hydrogen does have isotopes containing neutrons.