Final answer:
If Earth's rotation slowed down, then both days and nights would become longer without affecting the Earth's orbit around the Sun or the length of a sidereal day. Seasonal changes, which are due to the Earth's axial tilt, would not be influenced by the rotation speed.
Step-by-step explanation:
If the time it took for Earth to make one rotation around its axis increased, the length of both daytime and nighttime would become longer. The correct answer to the question is a) Days would become longer.
This is because Earth currently completes one rotation on its axis approximately every 24 hours, alternating exposure to sunlight and darkness across its surface. A longer rotation period would mean that any given point on Earth's surface would spend more time in sunlight and more time in darkness, leading to longer days and nights. It is important to note that this change would not affect the Earth's orbit around the Sun, which is a separate motion.
The Earth's orbit and the length of a sidereal day would not be affected by a change in Earth's rotational period. A sidereal day is the time it takes for Earth to rotate once relative to distant stars, independent of its orbit around the Sun. Similarly, the tilt of Earth's axis is responsible for the seasons.
If Earth's axis were not tilted, there would be minimal seasonal variation and the entire planet would experience roughly even lengths of day and night throughout the year. However, because Earth does have a 23.5° tilt, we experience significant seasonal changes.