The first part of iii) is asking you to 'Find the critical region for the test at the 10% signiﬁcance level, showing all of your calculations.'
a quick google search leads me to believe that 'The critical region of a hypothesis test is the set of all outcomes which cause the null hypothesis to be rejected in favor of the alternative hypothesis'
Your alternative hypothesis was done in the previous section of the question: H1: p > 0.2
where p is the probability.
Use distribution tables to see when the alternative hypothesis is true, i.e. which values of X. Those set of X values is the critical region that I have seen the mark scheme wants.