Step 1
Data needed: electronegativities from all atoms involved here
(Please, look them up in the periodic table)
C 2.55
O 3.44
N 3.04
Br 2.96
P 2.19
Cl 3.16
B 2.04
S 2.58
F 3.98
I 2.66
Step 2
Polarity is compared using the next formula:
ΔE = subtraction
e.g. for C-O ΔE = E oxygen - E carbon = 3.44 - 2.55 = 0.89 (most polar)
For C-N: ΔE = 3.04 - 2.55 = 0.49
So, for a. C-O <=== C-N
b. P-Br and P-Cl
ΔE (P-Br) = 2.96 - 2.19 = 0.77
ΔE (P-Cl) = 3.16 - 2.19 = 0.97
P-Br ===> P-Cl
c. B-O and B-S
ΔE ( B-O) = 3.44 - 2.04 = 1.4
ΔE (B-S) = 2.58 - 2.04 = 0.54
B-O <=== B-S
d. B-F and B-I
ΔE ( B-F) = 3.98 - 2.04 = 1.94
ΔE (B-I) = 2.66 - 2.04 = 0.62
B-F <=== B-I
Answer:
a. C-O <=== C-N
b. P-Br ===> P-Cl
c. B-O <=== B-S
d. B-F <=== B-I