A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Data Validation cannot prevent cells from being blank, so just use Data Validation of type List, with "Y" and "N" as values.
We'll use VBA to prevent cells from being cleared:
Right-click the sheet tab.
Select 'View Code' from the context menu.
Copy the following code into the worksheet module:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim cel As Range
If Not Intersect(Range("B:B"), Target) Is Nothing Then
For Each cel In Intersect(Range("B:B"), Target)
If cel.Value = "" Then
Application.EnableEvents = False
Application.Undo
Application.EnableEvents = True
MsgBox "Clearing cells in column B is not allowed!", vbExclamation
Exit For
End If
Next cel
End If
End Sub
Switch back to Excel and don't forget to save the workbook as a macro-enabled workbook (.xlsm).