If i used No2 on an engine eventually what would most likely give out first?

A) Rod
B) Crank
C) Piston
D) Rings
E) Other

This is if the engine is in good condition and properly tuned without ever experiencing detonation.

I don't know that is a question that really can be answered with accuracy. Those components all work in conjunction with one another,and when one goes another is usually going to follow. The closest I could come to answering that, is you will either lose your lower block or the upper. Also depends on how you are spraying your Nos, when, and how much is being sprayed I would think. Sorry I wasn't much help on that one.