Step 1: Understanding the Concept:
Nutritional deficiency syndromes link specific vitamin cofactors to characteristic clinical metabolic pathology.
Step 2: Detailed Explanation:
Evaluating the clinical deficiency pairs:
1. Body Fluid Accumulation (Edema), Beriberi - Vitamin B1 (Thiamine): Deficiency of thiamine impairs pyruvate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase, leading to energy failure, cardiovascular dysfunction with peripheral vasodilation, high-output cardiac failure, sodium-water retention, and edema (Wet Beriberi). This is the correct pair.
2. Rickets is caused by Vitamin D/Calcium deficiency (not Zinc).
3. Pus cells in milk indicates mastitis (bacterial infection).
4. Ketosis is an energy imbalance (carbohydrate/lipid deficiency).
Step 3: Final Answer:
Thus, the correct pair is Body fluid accumulation, beriberi - Vitamin B1, matching option (C).