The correct option is C 0 if f(i)−i>2,∀ i={1,3,5,7}
If i+f(i)<10,∀ i={1,3,5,7}
⇒f(1)<9,f(3)<7,f(5)<5,f(7)<3
So, in B={2,4,6,8}
1 has 4 choices
3 has 3 choices
5 has 2 choices
7 has 1 choice
∴ Number of required functions =4⋅3⋅2⋅1=24
If f(i)−i>2,∀ i={1,3,5,7}
⇒f(1)>3,f(3)>5,f(5)>7,f(7)>9
Element 7 in A have no choice in B.
∴ Number of required functions is 0.