Given below are two statements: Statement I: The concentration of…
2023
Given below are two statements:
Statement I: The concentration of chlorofluorocarbons (CFCs) in the atmosphere has increased in the past few years.
Statement II: CFCs already present in the atmosphere will persist for many years.
In light of the above statements, choose the correct answer from the options given below.
Answer: D. Statement I is false but Statement II is true — CONCEPTLong-lived atmospheric pollutants can decline in concentration after emissions are controlled while molecules already present remain for decades.…
- A.
Both Statement I and Statement II are true
- B.
Both Statement I and Statement II are false
- C.
Statement I is true but Statement II is false
- D.
Statement I is false but Statement II is true
Show answer & explanation
Correct answer: D
CONCEPT
Long-lived atmospheric pollutants can decline in concentration after emissions are controlled while molecules already present remain for decades. Atmospheric abundance and atmospheric lifetime therefore describe different aspects of the same pollutant.
APPLICATION
For Statement I, global monitoring shows that the atmospheric abundance of the major controlled CFCs peaked in the 1990s and has since declined after the Montreal Protocol curtailed emissions. Thus, an increase in the past few years is not the observed general trend for CFCs.
For Statement II, CFCs have atmospheric lifetimes measured in decades or longer. Molecules already released are removed only slowly, so they remain in the atmosphere for many years.
CONTRAST
The pattern Both Statement I and Statement II are true conflicts with the observed decline in major CFC abundance.
The pattern Both Statement I and Statement II are false conflicts with the long atmospheric residence of existing CFCs.
The pattern Statement I is true but Statement II is false conflicts with both the observed concentration trend and the long-lifetime evidence.
CROSS-CHECK
Emissions controls explain why concentration can fall, whereas long atmospheric lifetimes explain why ozone recovery is slow. These independent facts support Statement I as false and Statement II as true.
Therefore, Statement I is false but Statement II is true.