Hi

try

Code:
Option Explicit

Private Sub Workbook_BeforeClose(Cancel As Boolean)
    
    Dim r       As Range
    Dim k, i    As Long
    Dim msg     As String
    
    Const MySheet = "Sheet1"          '<<<<< adjust to suit
    Const MyRange = "A10:B45"          '<<<<< adjust to suit
    
    Set r = Worksheets(MySheet).Range(MyRange)
    
    If Application.WorksheetFunction.CountA(r) Then
        k = r.Value2
        msg = "Quantity missing in the following cell(s)"
        For i = 1 To UBound(k, 1)
            If Len(k(i, 1)) Then
                If Len(k(i, 2)) = 0 Then
                    msg = msg & vbLf & vbTab & r.Cells(i, 2).Address(0, 0)
                End If
            End If
        Next
        If InStr(1, msg, Chr(10)) Then
            MsgBox msg, vbInformation
            Cancel = True
        End If
    End If
    
End Sub