1. Create the drop-down list: First, create the drop-down list that you want to display in the cell. To do this, select the cell where you want to display the drop-down list, go to the Data tab in the ribbon, and click on Data Validation. In the Data Validation dialog box, select List from the Allow drop-down list, and enter the values for your list in the Source box. Click OK to create the drop-down list.
   
2. Write the IF statement: Next, write the IF statement that will determine whether to display the drop-down list or not. In this example, we want to display the drop-down list if cell A1 equals 100. So, in the cell where you want to display the drop-down list, enter the following formula:
   
   
   Formula:

   =IF(A1=100,INDIRECT("B1"),"") 

   In this formula, "B1" is the cell where you created the drop-down list. The INDIRECT function is used to reference the cell containing the drop-down list. If cell A1 equals 100, the formula will display the drop-down list in the cell. If not, the cell will be blank.
   
3. Test the formula: Finally, test the formula by changing the value in cell A1 to see if the drop-down list appears or disappears based on the condition.
   

That's it! You can now use an IF statement to display a drop-down list in a cell based on a condition.