What is the likeliest deficiency?

Vitamin B12 deficiency.

While vegans can suffer from an iron deficiency, resulting in anemia, it is more likely that a vegetarian suffers from an iron deficiency. The best answer to this question is B12 because eliminating all animal products puts vegans at great risk of a B12 deficiency, making them more prone to anemia.

Anemia is a condition diagnosed when a deficiency of red blood cells or hemoglobin results in pallor and weariness. To avoid illnesses like anemia, vegans should add foods rich in B12 or B12 supplements to their daily diet.