Which pair of molecules can form a hydrogen bond?

Question

Which pair of molecules can form a hydrogen bond?

Question 1 options:

CH4 and H2O

PF4 and NH3

NO2 and KF

Answer 1

For a hydrogen bond to occur, you need to have a hydrogen atom bonded to either a N, O or F atom.

CH₄ and H₂O: H2O has the required H but will not H-bond to CH4 because CH4 is non polar

PF₄ and NH₃: NH₃ has the required H and will form H-bonds with PF₄^-, but not sure what PF4 is

NO₂ and KF: No hydrogens present and so no H-bonds will form between these two