Question

Assertion: The mass number of Hydrogen is equal to its atomic number.

Reason: H-atom has no neutrons.

• A. Assertion is correct but reason is incorrect.
• B. The assertion is correct but the reason is incorrect.
• C. Both assertion and reason are correct and the reason is the correct explanation for assertion.
• D. Both assertion and reason are correct but reason is not the correct explanation for assertion

Answer 1

The correct option is C

Both assertion and reason are correct and the reason is the correct explanation for assertion.

Explanation for Correct Option:

Assertion:

1. Atomic number is defined as the number of protons in an atom's nucleus and the mass number is the total of the number of protons and neutrons.
2. Mass number$=$Number of protons$+$Number of neutrons.
3. The Hydrogen atom, written as ${}_1{}^1\mathrm{H}$ has an Atomic number and Mass number equal to one because we know there are no neutrons present in the hydrogen atom.
4. Also, we know that the number of protons is one because it is the same as the atomic number.

Explanation for the reason:

1. Mass number is defined as the total number of protons and neutrons.
2. Mass number$=$Number of protons$+$Number of neutrons.
3. Putting value for hydrogen we get, the number of neutrons$=$Mass number$-$Number of protons i.e. $1-1=0$
4. Hence, in a Hydrogen atom, there are no neutrons present.

Hence, Both assertion and reason are correct and the reason is the correct explanation for assertion.