Assumption 1: ann to tom are cells A1 to A6
Assumption 2: blank cell to david are cells B1 to B6
Select cells A1 to B6
Click “Home”->”Conditional formatting”->”Highlight Cells Rules”->”Duplicate Values”->click the drop down menu with the value “Duplicate”, change to “Unique”->click “OK”
Cell A4 with the value “mary” now has been highlighted in red