I was looking for a reverse voltage protection for the 100 ohm load in the circuit using an N-channel MOSFET, this is my design. The Zener diode is for gate voltage and of 5.1 volts, assuming the MOSFET wont turn on if the gate voltage is 0.7 volts, is the schematic topologically correct? (actual MOSFET parameters may not match)
If you are committed to using an n-channel FET, place it in series with the negative side of the voltage source. With the drain to the - input and the source to the load, this orients the internal body diode correctly for blocking a reverse voltage connection when the FET is off.
NOTE: The internal body diode actually is a zener diode, not a simple rectifier. If the reverse voltage is high enough, the diode will conduct. The zener conduction voltage always is greater than the FET's maximum drain-source voltage rating, and should be on the datasheet for the FET.
Here is an excerpt from an old project. When the correct voltage is applied. current through the load and the body diode creates a voltage drop across the load, which drives the source away from the + input and the gate, which turns on the FET, which shorts out the body diode for much better efficiency.
Here is a better symbol for the IRF530 (and most discrete n-channel MOSFETs):
If you reverse the 12V, then the body diode will conduct and you'll get most of the -12V across the load.
Swap drain and source on the IRF530 and run it "backwards", leave the zener connected G-S.