I will choose (a) Star and planet, and (b) Asteroid and comet to explain how they are different.
Stars and planets are fundamentally different in their characteristics and formation processes. A star is a massive celestial body that produces energy through nuclear fusion, which occurs in its core when hydrogen atoms fuse to form helium under extreme pressure and temperature. This process releases an immense amount of light and heat. In contrast, a planet is a smaller celestial body that orbits a star and does not produce its own light. Planets form from the dust and gas that surround a young star, accumulating material through gravity without undergoing nuclear fusion.
On the other hand, asteroids and comets are both small celestial bodies that orbit the sun, but they have distinct characteristics and origins. Asteroids are primarily composed of rock and metal and are mostly found in the asteroid belt between Mars and Jupiter. They are remnants from the early solar system that never coalesced into planets. Comets, however, are composed of ice, dust, and rocky material, and they typically originate from the colder outer regions of the solar system, like the Kuiper Belt or the Oort Cloud. When comets approach the sun, the heat causes their icy components to sublimate, creating a glowing coma and often a spectacular tail that points away from the sun, a feature not seen in asteroids.