To solve this problem, we need to understand the role of vitamins in the production of red blood cells (RBCs).$\newline$Red blood cell deficiency, often referred to as anemia, can be caused by a deficiency in certain vitamins.$\newline$Vitamin $B_{12}$ is crucial for the production of RBCs. It is involved in DNA synthesis, which is necessary for the formation of red blood cells.$\newline$A deficiency in vitamin $B_{12}$