Answer:
The addictive chemical of Nicotine.
Step-by-step explanation:
Nicotine, chemically speaking, is a colorless, oily, water-soluble, highly toxic, liquid alkaloid, C10H14N2, found in tobacco and valued as an insecticide.
Nicotine addiction occurs usually from smoking cigarettes or using other tobacco products. The chemical nicotine activates pleasure centers in the brain, releasing dopamine - see below - (neurotransmitter) and other chemicals that make you feel good. With repetition, pathways are created that connect smoking and the idea of "rewards". Changes take place in the brain that increase the sensitivity in brain receptors. Basically, the more you or someone else smokes, the more your brain believes that you not only want, but need, smoke.
Nicotine can cause a very common disease known as Lung Cancer.
Linkage:
⇒ Dopamine is a catecholamine neurotransmitter in the central nervous system, retina, and sympathetic ganglia, acting within the brain to help regular movement and emotion: its depletion may cause Parkinson's disease.
Parkinson's disease is a common neurologic disease believed to be caused by deterioration of the brain cells that produce dopamine, occurring primarily after the age of 60, characterized tremors, especially of the fingers and hands, muscle rigidity, shuffling gait, slow speech, and a masklike facial expression.