Correct Option
The correct option isDark, oily liquid with an unpleasant odour.
Explanation
Petroleum, derived from the Latin words petra (rock) and oleum (oil), is a naturally occurring fossil fuel found trapped in sedimentary rock formations. It is a complex mixture consisting primarily of hydrocarbons.
Detailed Analysis
- Physical State and Appearance: Crude petroleum is a dark, oily liquid. It is viscous (thick) in nature and varies in color from dark brown to black, or sometimes green, depending on its specific chemical composition.
- Odour: It has a characteristic unpleasant odour. This is largely attributed to the presence of various impurities, particularly sulfur-containing compounds, mixed with the hydrocarbons.
- Comparison with Other Options:
- It is not light-coloured or odourless; refined fractions like petrol or kerosene may be lighter, but crude oil is dark and pungent.
- It is not a solid rock-like substance; that description fits coal or oil shale.
- It is not a gaseous substance dissolved in water; while natural gas is often associated with it, petroleum itself is a liquid that floats on water due to being lighter and insoluble.
Key Takeaway
Crude petroleum is physically defined as a dark, viscous, oily liquid with a distinct unpleasant odour, serving as the raw material for various fuels and petrochemicals.