I will choose option (a) Star and planet, and option (b) Asteroid and comet.
Stars and planets are fundamentally different in their characteristics and formation processes. A star is a massive celestial body composed primarily of hydrogen and helium that undergoes nuclear fusion in its core, producing light and heat. This process allows stars to shine brightly and is responsible for their classification into various types based on size, temperature, and luminosity. In contrast, a planet is a smaller celestial body that orbits a star and does not produce its own light. Planets are formed from the residual material left over after the formation of a star, primarily through a process called accretion, where dust and gas in a protoplanetary disk gather together due to gravity.
Looking at option (b), asteroids and comets are also different in composition and origin. Asteroids are rocky, airless remnants left over from the early formation of our solar system, primarily found in the asteroid belt between Mars and Jupiter. They are composed mostly of metals and rock and do not possess any significant atmosphere. Comets, on the other hand, are icy bodies that originate from the outer regions of the solar system, such as the Kuiper Belt or the Oort Cloud. Comets are characterized by their tails that develop when they approach the Sun, causing their ice to sublimate and release gas and dust, creating a glowing head and a tail that points away from the Sun due to solar wind.