[vid]

there are some very good threads on this in the archives about the TIE in general, which I won't repeat except

1) just remember, you've been given a very wide topic
and
2) you won't get to explain every little nuance of your topic (nitrox) in ten minutes, so just concentrate on one element - and stick to that

for instance, you might talk about the practical impact of nitrox users diving with air users - max depth as per nitrox and deco as per air user - you can then highlight the STEP issues (and this particular topic is covered in DL and AD training subsequently)

I'm sure there'll be lots of suggestions from others on this and other suitable elements to consider

whatever element you choose - don't forget you need to set the scene, explain where your element fits in the wider topic and explain what'll happen next time

oh, and good luck
vid