Which of the following is not a chemical change ?

Options

A. Passing of steam over red hot coke.
B. Change in the colour of dilute nitric acid upon long standing.
C. Absorption of moisture by `P_(2)O_(5)`.
D. Absorption of moisture by `CaCl_(2)` .

Explanation

To determine which of the following options is not a chemical change, we need to analyze each option carefully.

### Step-by-Step Solution:

1. **Understand the Question**: We are looking for an option that represents a physical change rather than a chemical change. A chemical change involves the formation of new substances, while a physical change does not.

2. **Analyze the Options**:
- **Option 1: Passing of steam over red hot coke**: When steam (H2O) passes over red hot coke (carbon), it reacts to form carbon monoxide (CO) and hydrogen gas (H2). This is a chemical change because new substances are formed.

- **Option 2: Change in color of dilute nitric acid upon long standing**: A change in color indicates a chemical reaction has occurred, as the properties of the substance have changed and new substances may have formed. This is also a chemical change.

- **Option 3: Absorption of moisture by P2O5**: When phosphorus pentoxide (P2O5) absorbs moisture, it reacts with water to form phosphoric acid (H3PO4). This is a chemical change as well, since new substances are produced.

- **Option 4: Absorption of moisture by CaCl2**: Calcium chloride (CaCl2) absorbs moisture from the air but does not react chemically with it. Instead, it forms a hydrated complex without changing its chemical identity. This is a physical change.

3. **Conclusion**: After analyzing all the options, we find that the absorption of moisture by CaCl2 is the only process that does not result in a chemical change. Therefore, the answer is **Option 4**.

### Final Answer:
**Option 4: Absorption of moisture by CaCl2 is not a chemical change.**