Unfortunately, there is no built-in option in Excel to email a single worksheet as an attachment. However, there are a few workarounds you can use to achieve this.

One option is to copy the contents of the worksheet you want to send and paste them into a new workbook. Then, save this new workbook and attach it to your email. Here are the steps to do this:

1. Open the Excel workbook that contains the worksheet you want to send.
2. Right-click on the worksheet tab and select "Move or Copy".
3. In the "Move or Copy" dialog box, select "New Book" in the "To book" dropdown menu.
4. Check the "Create a copy" checkbox and click "OK".
5. This will create a new workbook with just the selected worksheet. Save this new workbook with a different name.
6. Open a new email message and attach the new workbook to the email.

Another option is to hide all the other worksheets in the workbook and then save and send the workbook. Here are the steps to do this:

1. Open the Excel workbook that contains the worksheet you want to send.
2. Right-click on the worksheet tab and select "Hide" for all the other worksheets in the workbook.
3. Save the workbook.
4. Open a new email message and attach the workbook to the email.
5. Instruct your friend to unhide the other worksheets if they need to access them.

I hope these workarounds help you send a single worksheet as an attachment in Excel.