Here is the full list of all 12 1 vs 100 achievements worth 200 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
Your team of four simultaneously achieves a Streak of three consecutive correct answers.
Answer a total of 500 questions.
Answer a total of 100 questions correctly.
Get three consecutive questions right while receiving an Instant Answer Bonus for each.
In a single round, receive six consecutive Instant Answer Bonuses.
In a single round, achieve a Streak of five consecutive correct answers.
In any single round, achieve a Streak of 12 consecutive correct answers.
Answer a total of 25 questions correctly.
In a single round, score a total of 1300 points through time bonuses.
Extended Play: In a single round, save up the maximum of three Skips.
In a single 1 vs 100 Live round, max out your Avatar Action 10 times.
Answer instantly and incorrectly three times in a row.