Assign the `R` and `S` configuration to the enantimers of `2`-bromobutane
Strategy: Identify the chiral carbon (stereocentre) and decide the order of priority for the four different ligands using `CIP` rules. Finally orient the molecule and designate the configuraiton.

Explanation

The structure of `2-`bromobutane is
`overset(1)CH_(3)overset(2)CH(Br)overset(2)CH_(2)overset(4)CH_(3)`
Step `1:` Carbon`-2`is the chiral carbon as it beasrs four different liagands. Carbons`-1` and `-4`bearing three hydogen atoms each and carbon`-3`bearing two `H` atoms cannot be chiral carbons.
Step `2:` The ligands bonded to chiral carbon are ethl`1(C_(2)H_(5))`, methy`1(CH_(3))`, bromine `(Br)` and hydorgen. It is easy to see that `Br gt C gt H` but this leaves the ordering of `CH_(2)H_(5)` and `CH_(3)` to be settled. Since it cannot be decided on the basis of the first atom (both `C`) then the next set of atoms have to be considered in order of precendence, i.e `C(HHH)` has to be compared with `C(CHH)`. Notice that theatoms in brackets are themselves listed in order of decreasing precedence. These are compared in turn and the first compatison `(H`and`C`)is enough to shown that `C_(2)H_(5)gtCH_(3)`. Thus the entire sequance is
`BR(1),C_(2)H_(5)(2),CH_(3)(3),H(4)`
Step `3:` The hydrogen atom has the lowest priority and is to be kept farthest from the viewer. Next the molecule is to be looked down thorugh the `C-H` bond.

The configuration assigned is based on the direction of the remaining three ligands as shown above.