An old man having complaint of anorexia, weakness and paraesthesia. On investigation, his haemoglobin was 5.8g% and peripheral smear showed macrocytes and neutrophils having hypersegmented nuclei. His tendon reflexes were also sluggish. Endoscopy revealed atrophic gastritis. Deficiency of which of the following factor can lead to this situation
Diagnosis of the patient is pernicious anemia. Factors favouring this diagnosis are:

Megaloblastic anemia.
Demyelination (decreased tendon reflexes)
Atrophic gastritis

So, he would require B12 supplementation.
Folic acid
Riboflavin
VitaminB12
None