Which of the following molecules has polar bonds but is a nonpolar molecule?
a. h₂
b. h₂o
c. nh₃
d. nacl
e. co₂
can anyone explain this one?

H2: non polar bond. non polar molecule
H2O: polar bonds, but there is a angle between 2 H-O bonds. so it's a polar molecule
NH3: polar bonds, but it's a stereochemical structure, like a pyramid with triangle base, N is the vertex. polar molecule.
NaCl: polar bond, polar molecule.(ion bond)
CO2: 2 O atoms are at two sides of C atom horizonally. giving CO2 a symmerical structure. it's nonpolar molecule with 2 polar bonds.

Exothermic,  physical change after it is already baked