The correct answer is (a) Monday.
A normal year has 365 days, which is divisible by 7, so the first day of the year will always be the same day of the week as the first day of the previous year. In a leap year, there are 366 days, which is not divisible by 7, so the first day of the year will be one day later than the first day of the previous year.
If the first day of the year is Sunday, then the last day of the year will be Monday. This is because there are 52 weeks in a year, plus one day. The 52 weeks are all seven days long, so the last day of the year will be one day after the first day of the year.
Option (b) is incorrect because Sunday is the first day of the year.
Option (c) is incorrect because Saturday is the day before the first day of the year.
Option (d) is incorrect because the answer is definitely one of the given options.