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 options given below:
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 options given below:
- (A)Both and are true but is NOT the correct explanation of
- (B) is false but is true
- (C)Both and are true and is the correct explanation of ✓ Correct
- (D) is true but is false
Answer: (C)
Solution
Hydrogen makes up about three quarters of the mass of the universe, yet the troposphere is dominated by nitrogen and oxygen and holds only traces of hydrogen, so Assertion A is true. Hydrogen is also the lightest element, its atom holding a single proton and a single electron, so Reason R is true. Because the molecule is so light, its average thermal speed at atmospheric temperatures is comparable with the escape velocity of the Earth, and hydrogen that reaches the upper atmosphere leaves the planet instead of accumulating in the troposphere, which is exactly what Assertion A records. Both A and R are true and R is the correct explanation of A.
JEE Main · 2021 · 24 Feb 2021 · Shift 2 · Single correct option