• Physical Partitioning of Minerals in Bovine Milk:
• Dual Phase Distribution:
• Milk minerals exist in dynamic equilibrium partly in the soluble phase and partly in the colloidal phase.
• Colloidal phase: Two-thirds of calcium, half of magnesium, and half of inorganic phosphate are bound within casein micelles as colloidal calcium phosphate (CCP).
• Soluble phase: One-third of calcium, sodium, potassium, chlorides, and soluble citrates/phosphates are dissolved in milk serum.
• Conclusion: Partly soluble and partly colloidal (Option 4).

Correct option: (4) Partly soluble and partly colloidal

• Partitioning of Calcium in Bovine Milk:
• Soluble vs Colloidal Distribution:
• Total calcium in bovine milk averages $120\text{ mg}/100\text{ mL}$ ($30\text{ mM}$).
• Approximately $33\%$ (one-third, $\approx 10\text{ mM}$) is present in the soluble serum phase as free ionic calcium ($\text{Ca}^{2+}$) and soluble complexes with citrate and phosphate.
• The remaining $67\%$ (two-thirds) is bound in the colloidal phase as colloidal calcium phosphate (CCP) within casein micelles.
• Conclusion: 33% (Option 4).

Correct option: (4) 33