Deficiency of Iodine causes:

Iodine is needed by the thyroid gland to make thyroxine (T4) and triiodothyronine (T3). When dietary iodine is short, the thyroid cannot make enough hormone. The pituitary then releases more TSH to push the gland harder, and the gland enlarges while trying to trap more iodine. That enlargement is goitre, so C is correct.

• A (Night blindness) is caused by deficiency of Vitamin A, which is needed for rhodopsin in the retina.
• B (Cancer) has no direct link to iodine deficiency. It is multifactorial and not a classic deficiency disease.
• D (Osteoporosis) is linked to calcium, Vitamin D and sex hormone changes, not iodine.

Core concept: iodine deficiency disorders (IDD) include goitre, hypothyroidism, cretinism and impaired cognitive development. The national IDD control programme and universal salt iodisation are the standard Mains and health-policy angle. Iodised salt is now the national norm, so the problem is largely controlled but still relevant.

Trap: candidates pick night blindness because vitamin deficiency questions blur together. Keep the mineral-to-disease pairs separate: iodine-goitre, iron-anaemia, calcium-osteoporosis, vitamin A-night blindness.