Scanning with Nmap and Zenmap

What is the switch that will make the utility run in passive mode?
           -p

Does null scanning work against a Microsoft Windows machine?
           no

Compare Nmap to Zenmap.
           Nmap is by far more powerful than Zenmap because it does not have the restrictions placed on it that Zenmap does by the GUI. The GUI does however make Zenmap far easier to use for simple commands because it does not involve all the work of memorizing tags and switches and the like. Zenmap basically just translates user input into Nmap commands. Zenmap will  probably be easier to use at first, but Nmap by itself will probably be far more flexible.