What is a possible physical sign of riboflavin deficiency?

Riboflavin deficiency, also known as vitamin B2 deficiency, can manifest through several physical signs, one of which is sore or pale lips. This symptom, also referred to as cheilosis, occurs because riboflavin plays a crucial role in maintaining healthy skin and mucous membranes. When there is an inadequate amount of riboflavin in the body, symptoms can appear in the form of mouth lesions and cracked lips.

The other options highlight symptoms associated with different nutrient deficiencies or conditions not necessarily tied to riboflavin specifically. For example, thin hair and night blindness is more commonly associated with deficiencies in other vitamins, such as biotin (for hair health) and vitamin A (for night vision). Small, yellow lumps around the eyes can relate to cholesterol deposits or other health issues but are not indicative of riboflavin deficiency.

Therefore, sore or pale lips stand out as a clear sign of riboflavin deficiency, making it a valid answer to the question. The other symptoms described are not directly linked to riboflavin, reinforcing the specificity of the chosen answer.