Using IF statements with Data Validation lists

In column A I have a Data Validation list. There's only three things on the list, lets call them option A, option B and option C.

Column B is dependent on column A. If option A is selected from the data validation list, I want column B to remain blank. But if option B or option C is selected from the data validation list, I'd like the text "N/A" to appear in column B. Is this possible? I've tried using an IF statement but it doesn't seem to be working.

I'm using Excel 2013.

Thanks in advance for your help

P.S my apologies if I have posted this in the wrong area