The correct option is D 10
In each row, the sum of the numbers in the first and the second column is equal to the number in the third column.
(i) In the first row, 6 + 1 = 7.
(ii) In the second row, 4 + 5 = 9.
Therefore, the number that will fill the empty slot in the third row = 8 + 2 = 10.