4 (c) Uracil. It is a pyrimidine base that only found on RNA.

Nucleotides are the building blocks of the nucleic acid. Purines and pyrimidines bases bind to ribose to form nucleoside, which when binded to phosphoric acid forms the nucleotides.

3 (b) Sucrose is an example of Oligosaccharide. It consists of a short chain of monosaccharide. It consists of one molecule of glucose and one molecule of fructose. Carbohydrates can be divided into three categories : Monosaccharide, Oligosaccharide and Polysaccharide.
 
Monosaccharides : They are simple sugar such as glucose and fructose.
 
Oligosaccharides : Consists of a small chain of monosaccharides. i.e. sucrose, maltose and lactose. They have to degraded into simple sugar in order to be absorb from the intestine. Degradation of sucrose gives one molecule of glucose and fructose, degradation of maltose gives two molecules of glucose, and degradation of lactose gives each molecule of galactose and glucose.
 
Polysaccharides : They consist of long chains of monosaccharides i.e. starch and glycogen

 2 (c). Cold cream is an example of W/O emulsion. It is a biphasic liquid dosage form, in which disperse phase and the dispersion medium are liquids. Emulsion is classified by five different categories:
 
Water in Oil (W/O) : Oil is continuous phase and water is a disperse phase, i.e. lotions and liniments.
 
Oil in water (O/W) : Water is continuous phase and oil is a dispersed phase i.e. most of the oral emulsions to unmask the oil taste of a medication.
 
Microemulsion : Unlike emulsions, microemulsion is a transparent with a small particle size. It is believed to be thermodynamically stable. The particle size of microemulsion lies between 10 to 200 nm. It is generally used for the solubilization of the drug in pharmaceutical dosage form.
 
Nanoparticles : As the name suggests, the particle size of this kind of emulsion is limited to nanograms. They are useful for the preparation of globulins and toxoids. Tetanus toxoid and human immunoglobulin G are examples of nanoparticles emulsion.
 
Multiple emulsions : Water in Oil in ware (W/O/W), Oil in water in Oil (O/W/O). The w/o/w emulsions are generally more preferable for preparation of various pharmaceutical dosage forms. They are used to prolong the duration of action of various drugs, to localize drug in the body and to prepare cosmetics.

1 (b) Benzyl alcohol is classified as a preservative. Preservatives prevent the growth of microorganisms and prevent deterioration of pharmaceutical dosage forms.

The ideal preservative must have the following characteristics: It must be effective against a broad spectrum of microorganisms. It must be stable for the lifetime of the product.

It must be nontoxic, soluble, palatable in test and odor and compatible with other ingredients in the formulation.

Commonly used preservatives:

* phenol * benzoic acid
* benzyl alcohol * chlorobutanol
* thiomersal * benzalkonium
* cresol * cetylpyridinium