Here is the full list of all 12 Counter-Strike: Global Offensive achievements worth 400 gamerscore.
Earn 100 awards
Get a kill with every weapon
Win an Arms Race match without dying
Personally kill the entire Terrorist team before the bomb is planted in Online Demolition Mode
Kill 250 enemies with headshots
Earn $50,000 total cash
Kill the entire opposing team without any members of your team taking any damage
Kill an enemy with the last bullet in your magazine (excluding sniper rifles and Zeus x27)
Inflict 2,500 total points of damage to enemies
Dominate an enemy
Kill 10,000 Enemies
Play 5,000 matches of Arms Race or Demolition mode