(a) Taking smack is considered as abuse because it is highly addictive drug. It is a depressant and slows down body functions. It can cause psychologicai and physical dependence. It causes constipation, nausea,/vomiting, lightheadedness, histamine launch, itching, xerostomia, excessive sweating, somnolence (sleepy or perhaps tired sensation), hypotension (reduced blood pressure), inspiration (sense of intensive satisfaction, pleasure, excitement along with joy), inflammation of the liver organ. 

(b) Chemical name of smack is diacetylmorphine. Its source plants is Papaver somniferum (poppy). 

(c) Syringe and needles are used to inject drugs usually intravenously so that the abusers can have the effects of drug very quickly and have a stronger effect. This mode of drug administration ensures availability of drug in higher amounts in the body which has increased chances of overdose which has proven fatal in most of the cases. Chances of addiction are higher in these cases. Infected syringes also predispose the user to catch diseases like AIDS.