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. A. Only one
2. B. Only two
3. C. All three
4. D. None

Answer: A

Explanation

Let’s analyze each pair:
1. **Cepheids**: These are variable stars that periodically brighten and dim, used as ‘standard candles’ to measure cosmic distances. The description ‘Giant clouds of dust and gas in space’ refers to nebulae. So, Pair 1 is incorrectly matched.
2. **Nebulae**: These are indeed giant clouds of dust and gas in space, often stellar nurseries where new stars form. The description ‘Stars which brighten and dim periodically’ refers to Cepheids. So, Pair 2 is incorrectly matched.
3. **Pulsars**: These are highly magnetized, rapidly rotating neutron stars that emit beams of electromagnetic radiation. Neutron stars themselves are formed from the gravitational collapse of massive stars after they exhaust their nuclear fuel. So, Pair 3 is correctly matched.
Therefore, only one pair is correctly matched. This question tests fundamental astronomical definitions, a common topic in Science & Technology.