Let's analyze each statement given in the question about chemical reactions.

Analyzing Statement I: Insoluble Salt and Precipitation Reactions

Statement I says: Insoluble salt is obtained by precipitation reaction.

A precipitation reaction is a chemical reaction that occurs when two soluble salts in aqueous solution are mixed, and an insoluble salt is formed. This insoluble salt then separates from the solution as a solid, which is called the precipitate.

For example, when a solution of silver nitrate (soluble) is mixed with a solution of sodium chloride (soluble), a precipitation reaction occurs:

$\text{AgNO}_3\text{(aq)} + \text{NaCl(aq)} \rightarrow \text{AgCl(s)} + \text{NaNO}_3\text{(aq)}$

Here, silver chloride ($\text{AgCl}$) is an insoluble salt and it forms a precipitate (solid). Sodium nitrate ($\text{NaNO}_3$) remains dissolved in the solution.

Therefore, Statement I is correct. Precipitation reactions indeed result in the formation of an insoluble salt.

Analyzing Statement II: Oxidation Definition

Statement II says: Addition of oxygen or loss of hydrogen is called oxidation.

Oxidation is a fundamental concept in chemistry, often described in several ways. One common way to define oxidation is in terms of the transfer of oxygen or hydrogen atoms:

• Addition of Oxygen: When a substance gains oxygen, it is said to be oxidized. For example, when carbon burns in oxygen, it forms carbon dioxide, and carbon is oxidized by gaining oxygen ($\text{C} + \text{O}_2 \rightarrow \text{CO}_2$).
• Loss of Hydrogen: When a substance loses hydrogen, it is also said to be oxidized. For example, ethanol ($\text{C}_2\text{H}_5\text{OH}$) can be oxidized to ethanal ($\text{CH}_3\text{CHO}$) by losing hydrogen atoms. ($\text{C}_2\text{H}_5\text{OH} \rightarrow \text{CH}_3\text{CHO} + 2\text{H}$).

These are classic definitions of oxidation, particularly in organic chemistry and earlier definitions of redox reactions.

Therefore, Statement II is correct. The addition of oxygen or the loss of hydrogen are indeed ways to define oxidation.

Conclusion on Correct Statements

Based on the analysis of both statements:

• Statement I: Insoluble salt is obtained by precipitation reaction - Correct.
• Statement II: Addition of oxygen or loss of hydrogen is called oxidation - Correct.

Both statements are correct descriptions of chemical processes.