What is the longest carbon chain in this molecule?
It is sure that you got parent chain 8 ie. correct.
But according to lowest set of locant rule,
the side group which gives lowest locant will be preferred until and unless a functional group is not present.
Counting from left
Location of Br = 4.
Location of Cl = 5.
So the sum of locations of Cl and Br is = 4+5 = 9.
counting from right
Location of Cl = 3
Location of Br = 5
So the sum of locations of Cl and Br is = 3+5 = 8.
Since we get lowest locant set on counting from right therefore the correct IUPAC name, maintaining the alphabetical order of prefix name, would be: