Question 5
For a hydrogen bond to form, the hydrogen atom must be attached to an atom of high electronegativity. Which atoms are these?
The right answer is the one marked above.
Fluorine, nitrogen or oxygen. These three are electronegative enough to leave the hydrogen atom with a large enough partial positive charge for a hydrogen bond to form.
Not every non-metal will do; carbon in particular is not electronegative enough, which is why methane forms no hydrogen bonds. Sodium and potassium are metals of low electronegativity, so they pull the other way entirely.