Concept:
A leap year has 366 days = 52 weeks + 2 extra days. These extra two consecutive weekdays occur 53 times.
Step 1: Analyze Statement I alone.
Given: 53 Mondays and 53 Tuesdays.
This means the extra two days are Monday and Tuesday.
So, the year starts on Monday.
Now, in a leap year:
\[
{Last day} = {First day} + 1
\]
So,
\[
{Last day} = {Tuesday}
\]
Thus, the last day is uniquely determined.
Statement I alone is sufficient.
Step 2: Analyze Statement II alone.
Only tells that it is a leap year, but starting day is unknown.
Statement II alone is NOT sufficient.
Step 3: Combine both statements.
Not required, since Statement I alone is sufficient.
Hence, Statement I alone is sufficient.