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?

1. Cepheids — Giant clouds of dust and gas in space: Incorrect. Cepheids are variable stars whose brightness changes periodically.
2. Nebulae — Stars which brighten and dim periodically: Incorrect. Nebulae are clouds of gas and dust in space.
3. Pulsars — Neutron stars formed when massive stars run out of fuel and collapse: Correct. Pulsars are highly magnetized rotating neutron stars, generally formed after the collapse of massive stars.

Thus, only one pair is correctly matched. My earlier selection of (b) was a mistake in mapping the count to the option; the analysis itself showed only one correct pair.