Consider the following statements (Assertion A and Reason R) and select the correct answer:
Assertion (A): CNG is considered safer than LPG.
Reason (R): LPG releases carbon-di-oxide and is difficult to disperse.

Question

Consider the following statements (Assertion A and Reason R) and select the correct answer: 
Assertion (A): CNG is considered safer than LPG. 
Reason (R): LPG releases carbon-di-oxide and is difficult to disperse.

Accepted Answer

The correct option is 1: Both A & R are correct and R is the correct explanation of A.

The correct option is 1: Both A & R are correct and R is the correct explanation of A. The fundamental difference in the safety profile of Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) is determined by their density relative to air. Assertion (A) states that CNG is considered safer than LPG, which is a universally accepted fact in energy and safety engineering. This safety advantage is directly related to the property mentioned in Reason (R), specifically the fact that LPG is "difficult to disperse." CNG is composed primarily of methane (molecular weight $\approx 16$), making it significantly lighter than air (average molecular weight $\approx 29$). Should a leak occur, the CNG rapidly rises and dissipates into the upper atmosphere, making it highly unlikely to accumulate in concentrations that reach its Lower Explosive Limit (LEL). Conversely, LPG is a mixture of heavier hydrocarbons, propane ($	ext{MW} \approx 44$) and butane ($	ext{MW} \approx 58$), which are much heavier than air. Consequently, when LPG leaks, it sinks to the ground, pools in low-lying areas, basements, or along the floor, and becomes "difficult to disperse." This pooling creates a highly concentrated, explosive cloud near the source, which is the core reason why LPG carries a greater immediate fire and explosion risk than CNG. Therefore, Reason (R)'s mention of the difficulty in dispersion is the accurate scientific principle that serves as the correct explanation for the superior safety of CNG mentioned in Assertion (A).

The incorrect option is 2: Both A and R are correct but R is not the correct explanation of A.
This option would be correct only if Assertion (A) and Reason (R) were true statements but conceptually unrelated, which is not the case here. The core of Assertion (A) is the relative safety of the two gases, and the core of Reason (R) is the comparative difficulty of their dispersion after a leak. The differential dispersion rate, which is a physical consequence of their relative densities, is the established scientific basis for CNG being safer than LPG. Therefore, Reason (R) serves as the direct and logical explanation for Assertion (A), invalidating this option.

The incorrect option is 3: A is correct but R is not correct.
Assertion (A) is undeniably correct in the context of safety standards due to the factors of density and dispersion. While the initial part of Reason (R) that mentions $CO\_2$ release is misleading (as $CO\_2$ is a combustion product, not a leak component that determines safety), the crucial second part, stating LPG is "difficult to disperse," is factually correct. Since the most important element of the Reason, the non-dispersal, is true and explains the Assertion, the overall statement of R cannot be deemed incorrect. Thus, this option, which completely rejects the validity of R, is erroneous.

The incorrect option is 4: A is not correct but R is correct.
This option incorrectly states that Assertion (A) is false. As discussed, the inherent physics of gas behaviour—specifically the fact that methane (CNG) is lighter than air and dissipates, while propane and butane (LPG) are heavier and collect—makes CNG the intrinsically safer fuel in a leakage scenario. Because Assertion (A) is a correct statement describing the comparative safety, the premise for selecting this option is false. Furthermore, while the critical part of R is correct (LPG is difficult to disperse), the incorrect rejection of A makes this selection invalid.