Step 1: Identify the condition - stomach disorders.
For stomach disorders such as acidity or indigestion, an antacid is needed. The ideal antacid should neutralize excess stomach acid (HCl) without causing harm.
Step 2: Identify Milk of Magnesia.
Milk of Magnesia is a suspension/colloidal dispersion of Mg(OH)2 (magnesium hydroxide) in water. It appears as a white, milky liquid - hence the name.
Step 3: Explain why it is a colloidal solution.
Mg(OH)2 is slightly soluble in water. When dispersed, it forms colloidal-sized particles (1-100 nm), making it a colloidal suspension rather than a true solution or coarse suspension.
Step 4: Mechanism of action.
Mg(OH)2 neutralizes excess stomach acid: \[ Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O \] The colloidal form provides a large surface area for this neutralization reaction, making it highly effective.
Step 5: Why colloidal form is beneficial.
The colloidal form of Mg(OH)2 coats the stomach lining more effectively than coarse particles, providing soothing relief. The large surface area of colloidal particles accelerates neutralization of HCl.
Step 6: Conclusion.
Milk of Magnesia (colloidal Mg(OH)2) is the colloidal solution used for stomach disorders as an antacid.
\[ \boxed{\text{Milk of Magnesia - Mg(OH)}_2 \text{ colloidal suspension (option 3)}} \]