Awesome and I think its a great idea to use the Distributions app for critical region. Unfortunately I hardly come here because all the stats functions are in the Statistics app. I wish this facility was integrared within the stats ap i.e. when performing Bonomial probablity calculations in stats ap we should be able to transition to this view...
Just pay close attention to the phrasing of the question here. “…ensure that the probability in each tail is as close as possible to 5%.” Hence the stated significance level is 10%