Halo: Combat Evolved/Vehicles

Scorpion
It is a slow-moving all-terrain tank. It has three weapons. The main one is the tank's turret: this fires an explosive round that does major damage, and works well against Banshees, Warthogs and other Scorpions, but it should not be used for any other Covenant. The second gun is the machine gun mounted on the right of the tank. Use this for smaller targets, and in-between reloading turret rounds. The third are the treads. They basically run over everything, but don't use them as a primary weapon as the tank moves very slowly. If you stop and let Marines get on, they will shoot at everything at which they can aim. All weapons on the Scorpion have unlimited ammunition.

Battling Scorpions
There are a couple of good ways to combat an enemy in a Scorpion tank:
 * The, hopefully, obvious way is to use a rocket launcher (or a FRG, if you are playing on PC) against an enemy Scorpion. Keep in mind however, that although tanks may drive slowly, you will still need to lead your shot to some extent, especially when firing from a long distance. One direct hit should kill under normal slayer rules.
 * If you can't get your hands on a rocket launcher, then probably an equally, if not better way, is to use a sniper rifle. There are gaps in the rollcage for the Scorpion, and so you should be able to hit the driver, if not score a headshot. Remember that experienced players will know better than to drive straight at you though, and will try to keep only their turret faced towards you, with the actual chassis of the tank facing the opposite direction.
 * If you wind up close to an enemy tank, try to use plasma grenades to destroy it, if you have them. You should only require two if you make direct latches, and if you don't have plasma grenades, throwing frag grenades under the tank will also do a fair amount of damage, but not as much as stickies would.
 * Another good way to take out an enemy tank is to use a Ghost vehicle. Because of the vehicle's stunning effect, the driver won't be able to turn as fast as he'd like, and so is rendered helpless as long as you don't overstrafe back into his turret's way. Also, even if that happens, it is considerably harder to kill a Ghost than another vehicle because of the fact that it hovers above the ground.
 * PC only: Should you wind up very close to an enemy Scorpion, then it is quite easy to just roast him with the flamethrower, provided you watch your step.
 * PC only: Also, you may use a Banshee to attack an enemy Scorpion in a fashion similar to that of the Ghost. However, keep in mind that you have a fuel rod cannon, which you can cause a large amount of damage with, but also, you have to fly out of the way, for the Banshee cannot strafe.

These aren't the only ways you can go about taking down an enemy tank, but rather, they are just tried-and-true methods for combatting these massive vehicles.