Question

Assertion: Calgon is used for removing \[C{{a}^{2+}}\]and \[M{{g}^{2+}}\] ions from hard water.
Reason: Calgon forms precipitate with \[C{{a}^{2+}}\] and \[M{{g}^{2+}}\] ions.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

Hint: The option has to be chosen according to the statements, if they are both correct still two options could be chosen. Calgon is just another name for a complex salt called sodium hexametaphosphate whose chemical formula is \[{{(NaP{{O}_{3}})}_{6}}\] .

Complete answer:
Calgon is a salt whose chemical name is sodium hexametaphosphate and whose chemical formula is \[{{(NaP{{O}_{3}})}_{6}}\] . It is used to normalize or soften permanent hard water for general purpose.
There are two types of hard water, temporary and permanent. Temporary hard water contains bicarbonate minerals which are the cause of the hardness. Permanent hard water contains high concentrations of anions such as sulphate and chloride anions which are the cause of the hardness.
Calgon is added in water to remove permanent hardness of the water. Calgon reacts with calcium chloride and magnesium sulphate dissolved in the water and forms complex compounds which get dissolved in the water.
Both the complex compounds formed by the reaction of Calgon with calcium chloride and magnesium sulphate dissolve in water and are not removed from the water. Thus, the statement in the assertion is incorrect.
Also, the complex compounds are dissolved in the water so there are no precipitates formed. Thus, the statement in the reason is also incorrect.
So, the correct option is option D, both assertion and reason are incorrect.

Note:
The reaction of Calgon and sodium chloride is shown below.
 \[2CaC{{l}_{2}}+N{{a}_{2}}[N{{a}_{4}}{{(P{{O}_{3}})}_{6}}]\xrightarrow{{}}N{{a}_{2}}[C{{a}_{2}}{{(P{{O}_{3}})}_{6}}]+4NaCl\]
Here, the sodium in Calgon substitutes the calcium in calcium chloride to form sodium chloride which dissolves in water easily. The reaction of Calgon with magnesium sulphate is shown below.
\[2MgS{{O}_{4}}+N{{a}_{2}}[N{{a}_{4}}{{(P{{O}_{3}})}_{6}}]\xrightarrow{{}}N{{a}_{2}}[M{{g}_{2}}{{(P{{O}_{3}})}_{6}}]+4NaS{{O}_{4}}\]
Here also, the sodium from Calgon substitutes the magnesium from magnesium sulphate to form sodium sulphate.