The most rigid substance among the options provided is the iron rod (b).
Here's why:
1. Rigidity: Iron is known for its strength and rigidity. An iron rod is a solid material that maintains its shape and structure under stress and external forces better than the other substances listed.
2. Comparing with the other options:
- Oil (a): Oil is a liquid and therefore lacks the rigidity of a solid material like an iron rod.
- Sulphuric acid (c): Sulphuric acid is a liquid as well and does not possess the same rigidity as a solid iron rod.
- Carbon monoxide gas (d): Carbon monoxide gas is in a gaseous state and has the least rigidity compared to solids or even liquids like oil and sulphuric acid.
In summary, an iron rod (b) is the most rigid substance among the options provided due to its solid nature and structural strength compared to oil, sulphuric acid, and carbon monoxide gas.
