Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: Hydrogen is the most abundant element in the Universe, but it is not the most abundant gas in the troposphere.

Reason R: Hydrogen is the lightest element.

In the light of the above statements, choose the correct answer from the given below

• A. A is false but R is true
• B. Both A and R are true and R is the correct explanation of A
• C. A is true but R is false
• D. Both A and R are true but R is NOT the correct explanation of A

Answer 1

The correct option is B

Both A and R are true and R is the correct explanation of A

The explanation for Assertion statement:

1. Hydrogen is the most abundant chemical substance in the universe, constituting roughly $75\%$ of all normal matter.
2. Since hydrogen is the only element without a neutron with just one proton and one electron specify it the simplest and most abundant element in the universe.
3. And in the troposphere, its presence is nearly about $0.00005\%$ due to which it is not the most abundant gas in the troposphere.

The explanation for Reason statement:

1. Hydrogen is the simplest and lightest element and the most common in the entire universe.
2. Since hydrogen atom has only $1$ electron and $1$ proton, the total mass of hydrogen is the smallest.
3. Thus, hydrogen is the lightest element.

Hence, option B is correct