A normal year has 365 days. A leap year has 366 days. In a normal year there are 52 complete weeks and one day extra. In a leap year there are 52 complete weeks and 2 days extra.
As no period of time has been specified, it can be taken that the extra two days of a leap year can be any two days of the week. The probability that one of them is a Monday is 2/7. The probability that one of them is not a Monday is 1 - 2/7 = 5/7
The correct answer is option A, 5/7