there is never a 100% chance, i have friends that have been in both branches for 10 years and never got deployed but then again i got deployed within weeks of graduating bootcamp
some of it depends on the job you pick, some jobs have low deployable rates, im in the infantry so it was only a matter of time for me anyway
pretty much guaranteed. Most people think "deployment" they think that they will be fighting in the war, but thats not the case. You can pretty much be deployed anywhere.
In the past recruiters have told people that it is 100%. The likelihood is very high. No, it's not 100%, but if you do join I would count on going. After all it is the purpose of the military.
No... nothing with the military will ever be 100% guaranteed. It all depends on what your MOS (military Occupational Specialty) is. If you are an infantrymen in the Army... there is a pretty good chance you will be deployed to a "Combative" area. If you are a weather man in the Air Force... well then, I don't know if you will be deployed. NOTE: I assume when you say deployed you mean to Iraq or Afghanistan. However you should know that deployed means sent to any other country besides the United States (traditionally). Even if you are deployed to Iraq or Afghanistan that does not mean you will be in Baghdad or where ever is a hotspot in Afghanistan.
I hope I helped you out. Thank you and good luck if you choose to serve.