Here is the full list of all 28 Bomb Defense achievements.
Level 6 completed.
Level 5 completed.
Level 4 completed.
Level 3 completed.
Level 2 completed.
Level 1 completed.
Earned 5+ gold medals by completing 5+ levels using as little money as possible.
Level 7 completed.
Level 8 completed.
Level 9 completed.
Level 10 completed.
Earned 10+ gold medals by completing 10+ levels using as little money as possible.
Level 11 completed.
Level 12 completed.
Level 13 completed.
Level 14 completed.
Level 15 completed.
Earned 15+ gold medals by completing 15+ levels using as little money as possible.
Level 16 completed.
Level 17 completed.
Level 18 completed.
Level 19 completed.
Level 20 completed.
Level 21 completed.
Level 22 completed.
Level 23 completed.
Level 24 completed.
Completed all levels using just about the least amount of money possible.