Hydrogen, oxygen and nitrogen are counted as some most important elements and found abundantly. About 75% of this universe is composed of hydrogen and helps different other matters to sustain. Large starts and planets, electrons and protons are also composed of hydrogen.
A sheet tab appears at the bottom of your worksheet. It has the name of the worksheet on it, which can be changed and you can also change its colour. This can be done by right clicking on it and picking the option from the shortcut menu that appears. By clicking a sheet tab, you can make that sheet the active sheet so that you can work on it.
The Prepare Tab in office button of Excel 2007 has been reorganized completely into Info Tab of File menu in Excel 2010. If you are going to take MOS 2010 Exam, it is better to take a look at the new locations: Properties: (The most hidden one) Now you can go to advanced properties with fewer click(s).