Sulfurous smog is formed throughans.Covalent processFree radical mechanismNone of theseIonic reaction

The formation of sulfurous smog is through a Free radical mechanism.

Here's a step-by-step explanation:

1. Sulfurous smog, also known as "London smog," is a type of air pollution that's a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles.

2. It is formed when sulfur dioxide (SO2) and nitrogen oxides (NOx) react with each other in the presence of a catalyst (like a free radical) and sunlight to form a dense, smoky fog.

3. The free radical mechanism is a chain reaction that involves the reaction of free radicals. Free radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration.

4. In the case of sulfurous smog, the free radicals are usually hydroxyl radicals (OH) or nitric oxide (NO) which react with sulfur dioxide to start the chain reaction.

5. The reaction continues to propagate and produce more and more smog until it is terminated by the reaction of two free radicals or by a reaction that removes free radicals from the system.

So, the correct answer is Free radical mechanism.