Here's how to apply data validation to a range of cells in Excel:

1. Select the Cell Range:

- Click and drag your mouse to highlight the entire range of cells where you want to restrict data entry.

2. Access Data Validation:

- Navigate to the "Data" tab on the Excel ribbon.
- In the "Data Tools" group, click the "Data Validation" button.

3. Set Up Validation Rules:

- In the "Data Validation" window, you'll see two main tabs: "Settings" and "Input Message" (optional).
- Settings Tab:
- Under "Allow," choose the type of data you want to restrict entry to. Common options include "Whole numbers," "Decimals," "List," "Date," and more.
- Depending on your chosen option, additional settings might appear. For example, if you select "Whole numbers," you could define a minimum and maximum allowed value.
- If you want to allow blank entries, keep the "Ignore blank" box unchecked.

4. Optional: Add Input Message

- The "Input Message" tab allows you to create a message that will appear when users select a cell in the defined range. This message can explain what kind of data is expected in the cell.
- Enter your informative message in the "Show input message when cell is selected" box.

5. Click OK to Apply

- Once you've configured the validation rules and any optional messages, click "OK" to apply the data validation to your selected cell range.

Now, when users try to enter invalid data in these cells, Excel will display an error message or prevent the entry based on your chosen validation criteria.