I guess you need to figure out something about the Binomial distribution. Therefore you should have
 as the number of trials (questions)
 as the probability of success (randomly guessing correctly)

and the last thing , in the probability notation the uppercase letter usually representing a random variable. So in this case it may just mean a Binomial random variable (which should be representing the number of questions guessed correctly). But if you want to represent the realized value of this random variable, then usually we will use the lowercase (which is the actual number of questions guessed correctly).