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?
Answer & explanation
Answer: (a) Only one
Only pair 3 is correctly matched. Pairs 1 and 2 have their descriptions swapped: Cepheids are stars whose brightness varies in a regular cycle, and nebulae are giant clouds of gas and dust. Pulsars are indeed neutron stars left when a massive star runs out of fuel and collapses.
- ✗ 1. Cepheids are pulsating variable stars, not clouds. Their regular changes in brightness are used to measure distances to galaxies.
- ✗ 2. A nebula is a very large cloud of gas (and dust), the place where stars form. It is not a star that brightens and dims.
- ✓ 3. A neutron star forms when a massive star runs out of fuel and its core collapses. Pulsars are neutron stars that spin fast and sweep a beam of radiation across space.
Remember · Cepheids are stars that brighten and dim in a regular cycle; nebulae are clouds of gas and dust; pulsars are spinning neutron stars.
📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 2 (practise this chapter)
Sources
- NCERT Class 11 · Fundamentals of Physical Geography, Chapter 2 “A galaxy starts to form by accumulation of hydrogen gas in the form of a very large cloud called nebula.”
- Cepheid Variables: Brightness Over Time (NASA Science, Hubble) ↗ “shows a class of pulsating star called a Cepheid Variable. Though rare, these stars are reliable distance indicators to galaxies.”
- Neutron Stars (NASA Imagine the Universe) ↗ “Neutron stars are formed when a massive star runs out of fuel and collapses. The very central region of the star – the core – collapses, crushing together every proton and electron into a neutron.”
Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·