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? 

(a) Only one 

(b) Only two 

(c) All three 

(d) None

9. Ans: a

Explanation:

Cepheids, also called Cepheid Variables, are stars which brigthen and dim periodically. This behavior allows them to be used as cosmic yardsticks out to distances of a few tens of millions of light-years

A nebula is a giant cloud of dust and gas in space. Some nebulae (more than one nebula) come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. 

Hence, 1st and 2nd pairs are incorrectly matched.

Pulsars are rapidly rotating neutron stars that blast out pulses of radiation at regular intervals ranging from seconds to milliseconds. 

A pulsar is the crushed core of a massive star that ran out of fuel, collapsed under its own weight and exploded as a supernova.

Hence, 3rd pair is correctly matched.

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