Your question is Biased Coin Identification. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
If you have a bag of coins where one coin is double-sided heads, how many flips would it take to be 99% sure you have drawn the biased coin? The answer is not unique unless the number of coins, the prior probability of selecting the double-headed coin, and the decision rule are specified. Derive the general Bayesian result, then evaluate the common equal-prior case where the selected coin is equally likely to be double-headed or fair and evidence consists of consecutive heads.