If the 21st of June 2021 was Monday, what day of the week was it on the 11th of June 2023?

Sunday

The 21st of June 2021 was Monday.

Remaining number of days in 2021 = 9 + 31 + 31 + 30 + 31 + 30 + 31 = 193

Divide 193 by 7 = 193/7 = 27 (Quotient), and 4 (Remainder)

Odd days in 2021 = 4days

Similarly, odd days in 2022 = 1day only

Now, the number of odd days in 2023 till 11 June => 3 + 0 + 3 + 2 + 3 + 4 = 15

Total number of odd days = 4 + 1 + 15 = 20

Divide 20 by 7; Remainder = 6, i.e., the required number of odd days = 6

So, on 11 June 2023, it will be Monday + 6 = Sunday

Thus, the 11th of June 2023 will be Sunday.