Excel 2010 does not have a specific maximum number of worksheets available in a workbook. The maximum number is limited by the amount of available memory in a system. The default setting is three sheets.
Excel does have limitations in other areas. For instance, the maximum worksheet size is 65,536 rows by 256 columns. Columns are no wider than 255 characters. The text in an individual cell must not exceed 32,767 characters. Fifty-six font colors are accessible in a workbook, and 4,000 different cell styles are available. A worksheet is allowed no more than 66,530 hyperlinks.
The “undo” function cancels out up to 16 levels of work.