The dehydration reaction of alcohols to generate alkene proceeds by heating the alcohols in the presence of a strong acid, such as sulfuric or phosphoric acid, at high temperatures. It involves carbonium ion in its mechanism.

Propionic acid and KOH reacts to produce potassium propionate.

$\underset{\mathrm{Propionic} \mathrm{acid}}{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH} } \stackrel{\mathrm{KOH}}{\to } \underset{\mathrm{Potassium} \mathrm{propionate}}{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOK}} + {\mathrm{H}}_2\mathrm{O}$

Gammexane is benzene hexachloride. Its IUPAC name is 1,2,3,4,5,6-hexachlorocyclohexane.

Saccharin is an artificial sweetner. It consists of carbon, hydrogen, sulphur, nitrogen and oxygen.

When aniline is treated with HCl and NaNO₂, it forms benzene diazonium chloride. Therefore, it gives diazo salt. 

Before using CHCl₃ as an anaesthetic, it is treated with aqueous solution of AgNO₃. A pure sample does not give ppt with aqueous AgNO₃.

Digestion of fat in intestines is aided by emulsification, i.e. breaking up of fat globules into much smaller emulsion droplets. The digestive enzyme, pancreatic lipase, is water soluble and can only work at the surface of fat globules. 

p-dichlorobenzene molecule has symmetrical structure. It can fit well in its crystal lattice. The intermolecular forces of attraction are strong. Hence, it possesses highest melting point among given options.

Calcium acetate on distillation produce acetone. It can be explained using the following reaction:

$\underset{\mathrm{Calcium} \mathrm{acetate}}{\mathrm{Ca}({\mathrm{CH}}_3\mathrm{COO}{)}_2 } \stackrel{\mathrm{Distillation}}{\to } \underset{\mathrm{Acetone}}{{\mathrm{CH}}_3{\mathrm{COCH}}_3} + {\mathrm{CaCO}}_3$

Nitro group (-NO₂) deactivates the benzene ring in nitrobenzene due to -M effect.