Which water-soluble vitamin is primarily found in muscle tissue of red meats?

The choice of B vitamins as the correct answer is based on the fact that red meat is a significant source of several B vitamins, including riboflavin (B2), niacin (B3), vitamin B6, and cobalamin (B12). These vitamins are essential for numerous metabolic processes, including energy production, red blood cell formation, and the proper functioning of the nervous system. Muscle tissue in red meats is particularly rich in these vitamins, making their presence notable in this food group.

Vitamin A, while important, is primarily found in liver and foods of animal origin as retinol, rather than muscle tissue. Vitamin K, mainly associated with blood clotting, is primarily found in green leafy vegetables and certain oils, not red meat. Vitamin C is abundant in fruits and vegetables but is not typically stored in muscle tissue of meats; it is also sensitive to heat and can be destroyed during cooking.

Thus, B vitamins are specifically and abundantly present in the muscle tissue of red meats, highlighting why this choice is the most fitting answer in the context of the question.