Q1.
(a) C5H9N3
(b) 
(c) The amine parts as N in amine is highly electronegative and are able to form hydrogen bonds with water.
Q2.
(a) C16H21N3
(b) The similarities are a two-carbon chain with a nitrogen at the end of both structures, and a three-atom sequence of N-C-N of both structures. The spatial placement of these groups seem similar too. The flat 5-ring of histamine is also similar to the flat 6-ring of the antihistamine. Given the similarities in structure, the antihistamine may bind to histamine receptor sites on cells more tightly than histamine itself, thus blocking histamine action.
Q3.
(a) Aspirin- produce a physiological response in the body
(b) Morphine- produce a physiological response in the body
(c) (Keflex) Antibiotic- inhibit the growth of substances that cause infections
(d) Estrogen- produce a physiological response in the body
(e) Amphetamine- produce a physiological response in the body
(f) Penicillin- inhibit the growth of substances that cause infections
Q4.
(a) Since they became widely available in 1994, the FDA and some independent researchers have found problems with some dietary supplements. Products like herbs are sometimes tainted with germs, pesticides, or toxic heavy metals. Other supplements do not contain what’s listed on the label. Still, others contain more or less than the amount of the herb listed on the label. And many have ingredients that aren’t listed on the label at all.
This problem extends beyond the supplement makers and sellers. Some herbal suppliers (those who grow, harvest, or sell the crops) may mix or even substitute their crops with less expensive or more readily available plants. There’s also the problem of accidental contamination, when one plant grows in with others, as well as cases of mistaken identity (when one plant looks like another). Given the global market, all of these problems can make it harder for a company to be sure that what they thought they were buying to make supplements is actually the herb they wanted.
In 2013, researchers in Toronto published a report in which they sampled and analyzed 44 herbal supplements. The supplements were sold in both the US and Canada, and labeled as containing single herbs. Using DNA bar coding analysis, less than half the supplements (48%) contained any of the herb listed on the label. More than half of the supplements contained something that wasn’t on the label (substitutions or fillers). Even among the samples that contained the herb on the label, many also contained fillers or contaminants.
(b) All Chinese Proprietary Medicines (CPM) i.e. products in the finished dosage forms (e.g. tablet, capsule, liquid) are regulated by the Health Sciences Authority (HSA) and must comply with a set of safety and quality criteria before they are allowed to be sold in Singapore. In addition, CPM dealers (importers, wholesale dealers and manufacturers) are also required to be licensed by HSA.