Consider the following pairs : Objects in space: Description 1. Cepheids: Giant clouds of dust and gas in space 2. Nebulae: Stars which brighten and dim periodically 3. Pulsars: Neutron stars that are formed when massive stars run out of fuel and collapse How many of the above pairs are correctly matched?
Explanation
* Pair 1 is incorrect: Cepheids are actually stars that brighten and dim periodically, not giant clouds of dust and gas.
* Pair 2 is incorrect: Nebulae are giant clouds of dust and gas in space, not stars that brighten and dim periodically. Thus, the first two pairs are reversed.
* Pair 3 is correct: Pulsars are rapidly rotating neutron stars that are formed when massive stars exhaust their fuel and collapse.
* So out of the 3 pairs given, only 1 pair (pair 3) is correctly matched.