How to Create a macro from drop down list (Validation List) in excel

Hi ,

In Excel I want to write a macro ....which will help me to generate
result based on the item selected from the Drop down List ( validation
List )
For Example :
In my Excel sheet A1 cell contains List ( 1,2,3,4) ...upon selecting 1
from A1 cell
In B1 cell Pass should be displayed and upon selecting 2 from A1 cell
Fail should be displayed ..Automatically with the help of macro...No
other Run button should be present...
Can anydoby share the macro code to do this

Thanks
Dasari Rajashekar