Which of the following has zero dipole moment? explain to me how to determine the answer. a. \(nh_3\). b. \(no_2\). c. \(pf_5\). d. \(hcn\)

Dipole moment of a compound is different from the dipole moment of a bond. You need to look at ALL bonds for the overall dipole moment of a molecule.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.