Full list of all 12 Zombie Apocalypse achievements worth 200 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
Kill a zombie using an environmental hazard in any game mode
Complete an entire arena, getting every kill with the Chainsaw
Kill at least one zombie with each weapon type in any game mode
Kill 10 or more zombies at the same time in any game mode
Play in an online multiplayer game
Complete each arena at least once in the same game in any game mode
Rack up a 100x multiplier in any game mode
Save 25 survivors in any game mode
Kill 25 zombies in any game mode using environmental hazards
Complete 7 days in any game mode without dying
Complete the final day of the "7 Days of Hell" unlockable mode
Complete the Final Day, in either Single or Multiplayer, and finish the game