Question

__________ water does not lather with soap.
A. Hard water
B. Soft water
C. Contaminated water
D. None of the above

Answer 1

Hint: Lather with soaps means the ability to form foam when soap dissolves in water. Water has several types depending on the type of minerals it contains. The concentration of certain minerals creates the ‘hardness’ of water. These certain minerals are salts of calcium and magnesium as bicarbonates, chlorides, and sulphates.

Complete answer:
Let us discuss this question option-wise to find the correct answer:
A. Hard water:When hard water is treated with soap solution, it forms a white curdy precipitate known as scum. When soap is added to hard water, the $\text{C}{{\text{a}}^{+2}}$ and $\text{M}{{\text{g}}^{+2}}$ ions present in hard water react with soap. Soaps contain the sodium salts which are converted to their respective calcium and magnesium salts which are precipitated as scum. When the scum dries on washed clothes it makes them stiff and uncomfortable. So, hard water does not form lather with soap.
B. Soft water: The main reason for hardness in water is the presence of $\text{C}{{\text{a}}^{+2}}$ and $\text{M}{{\text{g}}^{+2}}$ ions. Soft water is a term for water which does not have dissolved calcium and magnesium. As soft water has few calcium ions, there is a lathering action of soaps and no scum is formed in normal washing. Moreover, soft water produces no calcium deposition in water heating systems.
C. Contaminated water: Water is said to be contaminated when it contains microorganisms like bacteria that get in the water from human or animal excreta. It can contain chemicals from industrial waste. Fertilizers contain nitrates which can enter the water with runoff from the land. It has no relation with the hardness of water.
Hard water does not lather with soap.

So option ‘a’ is the correct answer.

Additional Information:
Hard water can is not good for daily use:
(1) Hard water contributes to dry skin and hair. Washing your hair frequently with hard water will leave your scalp feeling itchy.
(2) Hard water also changes the pH balance of your skin, weakening it as a barrier against infections. People with eczema are more vulnerable.

Note:
The answer of this question can be directly estimated by writing differences between the two:

SOFT WATER	HARD WATER
Have low mineral content	Have high mineral content
Contains sodium ions	Contains calcium and magnesium ions
Obtained by passing hard water over an ion exchange resin	Formed when water is mixed with chalk and limestone
Tastes salty	Have a characteristic taste
Forms foam with soap.	Does not form lather, but a film is formed over the surface

So, it is clear that soft water forms lather but hard water does not.