The addictive, colorless, and highly volatile alkaloid in tobacco is:

• A. Tar
• B. Biogene
• C. Nicotine
• D. All of the above

Answer: (C)

The key idea here is identifying the substance in tobacco that drives dependence and fits the clues of being an alkaloid that is colorless and highly volatile. Nicotine is the primary addictive alkaloid in tobacco. In its pure form it is colorless and is highly volatile, which helps it vaporize and reach the brain quickly when tobacco is smoked. This rapid onset of effect reinforces the habit and makes nicotine especially addictive.

Tar, by contrast, is not an alkaloid. It’s a sticky mixture of combustion byproducts that tobacco smoke leaves behind, not the chemical responsible for addiction. Biogene isn’t a recognized tobacco alkaloid, so it doesn’t fit the description either. Therefore nicotine best matches all the clues and is the correct answer.