Which of the following are chemical changes?
(i) Decaying of wood
(ii) Burning of wood
(iii) Sawing of wood
(iv) Hammering of a nail into a piece of wood

Options

A. (i) and (ii)
B. (ii) and (iii)
C. (iii) and (iv)
D. (i) and (iv)

Explanation

To determine which of the following are chemical changes, we need to analyze each option based on the definition of a chemical change. A chemical change involves the formation of new substances that are different from the original substances, and these changes are usually not reversible.

Let's evaluate each option step by step:

1. **Decaying of wood**:
- **Analysis**: Decaying of wood is a process where wood breaks down due to the action of bacteria and other decomposers. This process results in the formation of new substances (like simpler organic compounds).
- **Conclusion**: This is a chemical change.

2. **Burning of wood**:
- **Analysis**: When wood burns, it reacts with oxygen in the air to produce ash, smoke, and carbon dioxide. This reaction changes the wood into entirely different substances, and it cannot be reversed.
- **Conclusion**: This is also a chemical change.

3. **Sawing of wood**:
- **Analysis**: Sawing wood involves cutting it into smaller pieces. This process does not change the chemical composition of the wood; it remains wood regardless of its size.
- **Conclusion**: This is a physical change.

4. **Hammering of a nail into a piece of wood**:
- **Analysis**: Hammering a nail into wood changes the shape and position of the nail but does not alter the chemical composition of either the nail or the wood.
- **Conclusion**: This is a physical change.

**Final Answer**: The chemical changes among the options are (i) Decaying of wood and (ii) Burning of wood.