According to Stat Trek, for an expression to be binomial, it must consist of a certain number of repeated trials and can only result in two possible outcomes.
Taking A, this isn’t right as we don’t have a certain number of phones that we’re going to record the number of defective phones of. The same applies with D. Between B and C, we know that there has to be a certain number of trials. We don’t know how many trials it will take (for a fact) to find 200 defective phones, but we do know that if we select 200 phones, there will only be 200 trials. Therefore, the answer is C.
Please note that these only have two options, defective or not defective, so that isn’t an issue here.
Feel free to ask further questions!