Consider the following pairs:Objects in space Description1.Cepheids : Giant clouds of dust and gas in space2.Nebulae : Stars which brighten and dim periodically3.Pulsars : Neutron stars that are formed when massive stars run out of fuel and collapseHow many of the above pairs are correctly matched?

1. A

   Only one

   Only one pair. Pulsars are spinning neutron stars from core collapse. Cepheids are not dust clouds; nebulae are not periodic variable stars — those two labels are swapped.

2. B

   Only two

   Only two. Cepheids and nebulae are reversed.

3. C

   All three

   All three. Two of three rows are inverted.

4. D

   None

   None. The pulsar row is correctly matched.

Summary. Official key is (a) only one. Pulsars are rapidly rotating neutron stars left when massive stars collapse. Cepheids are variable stars (period–luminosity). Nebulae are clouds of gas and dust. Pairs 1 and 2 swap those meanings.