Question

Which of the following is used as purgative?
A) ${\text{HgS}}$
B) ${\text{H}}{{\text{g}}_2}{\text{C}}{{\text{l}}_2}$
C) ${\text{HgC}}{{\text{l}}_2}$
D) ${\text{ZnS}}{{\text{O}}_{\text{4}}}$

Answer 1

Hint: The substances which loosen the stools and increase the bowel movement are known as purgatives. Another name for purgative is laxative. Purgatives are used to treat and prevent constipation.

Complete answer:
Mercury chloride or calomel is mainly used as purgative. The molecular formula of mercury chloride is ${\text{H}}{{\text{g}}_2}{\text{C}}{{\text{l}}_2}$.
Mercury chloride is a saline purgative. Mercury chloride is non-absorbable and an osmotically active substance. It attracts and retains water in the intestines. Mercury chloride increases intraluminal pressure which stimulates bowel movement.
Mercury chloride increases intestinal motility by leading to the release of cholecystokinin.

Thus, the correct option is (B) ${\text{H}}{{\text{g}}_2}{\text{C}}{{\text{l}}_2}$.

Additional Information: Other uses of mercury chloride are as follows:
> Mercury chloride is used in photography, disinfectants, wood preservatives, fungicides, etc.
> Mercury chloride is used as an antiseptic.
> Mercury chloride is used in the preservation of anatomical specimens, leather tanning, ant repellent, etc.
> Mercury chloride is very heavy and soft in nature. It is white coloured in appearance. It is tasteless and odourless. Mercury chloride is very toxic when absorbed in high amounts.

Note: Purgatives alter the fluid and electrolyte balance in the body. The small and large intestines are the main site of action of purgatives. It requires half to three hours for the onset of action of purgatives. Purgatives treat and prevent constipation. High doses of purgatives can lead to diarrhoea. Thus, limited doses of purgatives must be consumed. Some examples of purgatives are cascara, buckthorn, senna extract, aloe vera, phenolphthalein, bisacodyl, castor oil, etc.