Out of the following which is basic in nature?

Milk of magnesia

The correct answer is option 3. Milk of magnesia.

Milk of magnesia, chemically known as magnesium hydroxide (\(Mg(OH)_2\)), is a basic or alkaline substance. It is derived from magnesium oxide, which is a white solid mineral commonly found in nature.

When milk of magnesia is dissolved in water, it undergoes dissociation into magnesium ions (\(Mg^{2+}\)) and hydroxide ions (\(OH^-\)). The hydroxide ions give the solution its basic properties.

\[ Mg(OH)_2 \rightarrow Mg^{2+} + 2OH^- \]

The hydroxide ions (\(OH^-\)) from the dissociation of milk of magnesia can react with excess stomach acid (hydrochloric acid, \(HCl\)) in the stomach to form water and magnesium chloride (\(MgCl_2\)):

\[ 2HCl + Mg(OH)_2 \rightarrow 2H_2O + MgCl_2 \]

This neutralization reaction helps to reduce the acidity in the stomach, providing relief from symptoms of indigestion, heartburn, and acid reflux.

In summary, milk of magnesia is basic in nature due to the presence of hydroxide ions (\(OH^-\)) produced upon its dissociation in water. It acts as an antacid by neutralizing excess stomach acid, making it effective in alleviating gastrointestinal discomfort.