Answer:
When the population variance is known and the sample size is small, the distribution used to identify the rejection region is the t-distribution. The t-distribution is specifically designed for small sample sizes when the population standard deviation is unknown. It is similar to the normal distribution but has fatter tails, which accounts for the increased uncertainty associated with smaller sample sizes. The t-distribution is used in hypothesis testing and constructing confidence intervals when working with small samples, providing more accurate results compared to the standard normal distribution