Question

Which ion does not cause hardness in water?

• A. Calcium
• B. Magnesium
• C. Sodium
• D. Iron

Answer 1

The correct option is C

Sodium

The explanation for the correct option:

C) Sodium

• When Calcium and Magnesium salts such as hydrogen carbonate, chloride and sulphate are present in water, they cause the hardness of the water.
• It does not lather with soap.
• Sodium salts of sulphates or chlorides are soluble in water and thus, do not cause hardness in water.

The explanation for the incorrect options:

A) Calcium

• Salts of Calcium in the form of sulphates, chlorides and hydrogen carbonates are insoluble in water and form precipitates thus, wasting a lot of soap.
• Hence, it causes the hardness of the water.

B) Magnesium

• Salts of Magnesium in the form of sulphates, chlorides and hydrogen carbonate are insoluble in water and form precipitates thus, wasting a lot of soap.
• Hence, it causes the hardness of the water.

D) Iron

• Salts of Iron in the form of sulphates, chlorides and hydrogen carbonates are insoluble in water and form precipitates thus, wasting a lot of soap.
• Hence, it causes the hardness of the water.

Hence, option (C) is correct. Sodium-ion does not cause the hardness of the water.