To find out the electronegativity of each pair, work it out by listing them. 
H = 2.2 
S = 2.1 
N = 3.0 Cl = 3.0 
O = 3.5 
C = 2.5 
 
H – S -> 2.2 - 2.1 = 0.1 
H – Cl -> 2.2 - 3.0 = -0.8 
N – H -> 3.0 - 2.2 = 0.8 
O – H -> 3.5 - 2.2 = 1.3 
C – H-> 2.5 - 2.2 = 0.3 
So, the pairs that has the highest electronegativity is H-Cl and N-H.