Final answer:
A planet could remain in the habitable zone longer around a star with a temperature of 4,500K compared to the Sun, because a lower temperature usually indicates a less massive star which has a longer main sequence lifetime.
Step-by-step explanation:
The question focuses on which type of star could have a planet in the habitable zone for a longer period than a planet around the Sun. As the main-sequence lifetime of a star is greatly dependent on its mass, less massive stars tend to have longer lifetimes, which in turn could allow a planet to remain in the habitable zone for a longer time.
Considering the options given and the information about main-sequence lifetimes:
- A star with a temperature of 4,500K has a lower mass than the Sun and thus a longer main sequence lifetime.
- A star with a mass of 2 solar masses would have a shorter lifetime than the Sun.
- A star with a main-sequence lifetime of 5 billion years would have a shorter lifespan than the Sun.
- A star with a temperature of 6,500K is more massive and would not have a longer habitable zone duration than the Sun.
Therefore, the correct answer is a) A star with a temperature of 4,500K, as it implies a lower mass and a longer main sequence lifetime.