Which is a physical sign of iodine deficiency?

The correct answer, thyroid enlargement, is a well-known and recognized physical sign of iodine deficiency. Iodine is an essential nutrient for the synthesis of thyroid hormones, which are critical for regulating metabolism and various bodily functions. When there is insufficient iodine in the diet, the thyroid gland responds by enlarging in an attempt to capture more iodine from the bloodstream, leading to a condition known as goiter. This enlargement is a physiological adaptation to low iodine levels, which underscores the importance of adequate iodine intake for maintaining normal thyroid function.

The other choices describe health conditions that are not specifically linked to iodine deficiency. Swollen or bleeding gums and skin bleeding can result from vitamin C deficiency or other nutritional deficiencies. Gray-brown spots on the teeth are typically associated with fluorosis or other dental issues and do not relate to iodine. Thus, while those conditions indicate various health issues, they do not represent physical signs of iodine deficiency, reinforcing that thyroid enlargement is the direct and relevant indicator for this nutritional deficiency.