Small amount of iodine is added to common salt so that

The correct option is C

Occurrence of goitre is prevented

The correct option is C:

Explanation of the correct option :

Goitre is caused by the deficiency of iodine in the diet. Iodine is necessary for the synthesis of the thyroxine hormone. A small amount of iodine is added to common salt so that occurrence of goitre is prevented.

Explanation of the incorrect option:

Option A:

Edema is usually caused by: standing or sitting in the same position for too long. eating too much salty food, and being overweight.

Option B:

Common salt can be utilized without adding iodine.
Option D:

The kidney does not require iodine for being efficient in maintaining water balance.

Final answer: Small amount of iodine is added to common salt so that occurrence of goitre is prevented.