A leap year has 366 days = 52 weeks + 2 extra days. The 2 extra days can be: (Sun,Mon), (Mon,Tue), (Tue,Wed), (Wed,Thu), (Thu,Fri), (Fri,Sat), (Sat,Sun) - 7 cases. Favourable for 53 Sundays or 53 Saturdays: (Sun,Mon), (Fri,Sat), (Sat,Sun) = 3 cases. Probability =73.
Note: The chosen option 3 (1/7) is incorrect; the correct answer is option 1 (3/7).