Low visibility during cold weather is due to (b) unburnt carbon particles or hydrocarbons suspended in air.
Explanation: When fossil fuels are burnt, they release unburnt carbon particles and hydrocarbons into the atmosphere, which can accumulate and reduce visibility, especially in cold conditions where water condenses and forms fog.
Why other options are incorrect:
(a) formation of fossil fuel: While the burning of fossil fuels causes the release of unburnt carbon particles, the actual low visibility is due to the presence of these particles in the air, not the process of fossil fuel formation.
(c) lack of adequate power supply: This doesn’t directly relate to air quality or visibility.
(d) none of these: This is incorrect as option (b) is the correct explanation.