Question

It is recommended to keep an automobile's petrol tank full or nearly full at all times. Which of the options could be the reason(s) for this recommendation?

• A. A full tank prevents moisture from condensing in the petrol tank.
• B. In an empty petrol tank, dirt or rust may get trapped easily, which can block the fuel filter.
• C. Keeping the tank full would leave less air in the tank, thus reducing the evaporation rate of the petrol.
• D. The weight of a full petrol tank is less than 3% of the weight of the automobile, and hence the loss of fuel efficiency due to this extra weight is negligible.

Hint:

In general knowledge questions about practical advice, consider all related factors, including the primary reasons for the advice and any common counterarguments or trade-offs involved.

Answer 1

The Correct Option is A, B, C, D

Step 1: Understanding the Concept:
The question asks for the scientific and practical reasons behind the advice to keep a car's fuel tank full. This involves understanding basic principles of physics and automotive maintenance.
Step 2: Detailed Explanation:
Let's analyze each option:
A. A full tank prevents moisture from condensing in the petrol tank. This is a primary reason. The empty space above the fuel in a tank is filled with air, which contains water vapor. When the temperature drops, this vapor can condense into liquid water. Water in fuel can cause rust and engine problems. A full tank minimizes the volume of air, thus minimizing the amount of water that can condense. This is true.
B. In an empty petrol tank, dirt or rust may get trapped easily, which can block the fuel filter. This is also a valid concern. Moisture (as mentioned in A) can cause the steel tank to rust from the inside. Running the tank low can also cause the fuel pump to pick up sediment and rust particles that have settled at the bottom, potentially clogging the fuel filter and damaging the pump. This is true.
C. Keeping the tank full would leave less air in the tank, thus reducing the evaporation rate of the petrol. This is also true. In a sealed container, a liquid will evaporate until the air above it is saturated with its vapor (reaching vapor pressure equilibrium). With less air space (ullage) in a full tank, this equilibrium is reached with less total fuel having to evaporate compared to a near-empty tank. This reduces fuel loss and emissions. This is true.
D. The weight of a full petrol tank is less than 3% of the weight of the automobile, and hence the loss of fuel efficiency due to this extra weight is negligible. This statement addresses a common counterargument. While it is true that carrying more weight (a full tank of fuel) technically reduces fuel efficiency, this statement correctly points out that the effect is negligible for a typical car. While not a direct reason *to* keep the tank full, it's a valid part of the overall consideration, arguing that the benefits (A, B, C) outweigh this minor drawback. In the context of multiple-correct-answer questions, such relevant factual statements are often considered correct.
Step 3: Final Answer:
Options A, B, and C are direct reasons for the recommendation. Option D is a valid supporting argument that dismisses a potential downside. All are correct in the broader context of the recommendation.