There are a total of 33 Intels in Call of Duty: Black Ops 2. Each Story Mission has exactly 3 intels. Once collected they are saved automatically and will not appear again. After collecting them you have to complete the entire mission! The game will not recognize your progress otherwise. Even after collecting the last intel the High IQ trophy / achievement will not pop until the mission is over. Obtaining every intel of a mission is also a requirement for the challenges. Completing challenges unlocks new perks and awesome weapons! In your Carreer Record you can see if you've found all the intels of a mission.