The number of pair of positive integers whose sum is 99 and HCF is 9 is:

Given, HCF of two numbers = 9

Let the two numbers be $$9x$$ and $$9y$$

Sum of the numbers = 99

$$=$$> $$9x+9y=99$$

$$=$$> $$9\left(x+y\right)=99$$

$$=$$> $$x+y=11$$

$$=$$> The pair of positive integers which satisfies the above condition is (1,10) (2,9) (3,8) (4,7) (5,6)

$$=$$> The possible pair of numbers are (9,90) (18,81) (27,72) (36,63) (45,54)

$$\therefore\ $$The number of positive pair of integers = 5

Hence, the correct answer is Option D