Question

# The deliquescent among the following is:                   (A)$CaC{l_2}$                    (B)$FeS{O_4}.7{H_2}O$                    (C)$CuS{O_4}.5{H_2}O$                    (D)$BaC{l_2}.2{H_2}O$

Hint: This substance has the ability to absorb water from surroundings and form a solution by dissolving in it. It is also used as an effective ice melter than rock salt (NaCl).

-They are usually salts, for example: potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium chloride ($N{H_4}Cl$), calcium chloride ($CaC{l_2}$), etc.
-Calcium chloride ($CaC{l_2}$) is highly hygroscopic, attracts moisture from its surroundings very strongly and it releases a large amount of heat in an exothermic reaction on dissolving in water. Thus, making it a good deliquescent material.
It is formed by neutralising hydrochloric acid (HCl) with calcium hydroxide ($Ca{(OH)_2}$) and can be found in various hydrated forms of $CaC{l_2}.x{H_2}O$ where x can be 0, 1, 2, 4 or 6.
Note: For any substance to be deliquescent it must have the ability to absorb a large amount of water and be sufficiently soluble to dissolve in it. Calcium chloride has both and also is exothermic with water which makes it highly useful in melting ice on sidewalks, roads, etc. It can cause depression in the freezing point and prevent freezing at temperatures even ($- {52^ \circ }C$) low.