In queuing problems, which of the following probability distributions is typically used to describe the number of arrivals per unit of time?

A) binomial
B) normal
C) Poisson
D) exponential
E) lognormal

The Poisson distribution is used to describe the number of arrivals per unit of time in queuing problems, where the arrivals are random and independent of each other. This distribution is appropriate when the arrival rate is constant and the arrivals are rare or infrequent. The binomial distribution is used to describe the number of successes in a fixed number of trials, which is not applicable in queuing problems. The normal and lognormal distributions are used to describe continuous variables, whereas the number of arrivals is a discrete variable. The exponential distribution is used to describe the time duration between arrivals or service times, rather than the number of arrivals.