Step 1: Classification of vitamins.
Vitamins are divided into fat-soluble (A, D, E, K) and water-soluble (B-complex and C) based on their solubility.
Step 2: Fat-soluble vitamins.
Vitamins A, D, E, and K dissolve in non-polar organic solvents and accumulate in lipid-rich tissues. They are not excreted rapidly.
Step 3: Water-soluble vitamins.
Vitamins B (all members: $B_1$, $B_2$, $B_6$, $B_{12}$, niacin, folic acid) and Vitamin C dissolve readily in water. They are not stored significantly and need regular dietary intake.
Step 4: Conclusion.
Among the options, Vitamin B is water-soluble.
\[ \boxed{\text{Vitamin B}} \]