Rank the following compounds in order of decreasing boiling point: potassium fluoride (kf), carbon tetrafluoride (cf4), and formaldehyde (ch2o)

Ranking of given compounds in order of decreasing boiling point : KF  > Formaldehyde > Carbon tertrafluoride

Explanation:

KF is an ionic compound. Hence ionic force is between KF molecules.Formaldehyde is a polar compound due to presence of polar carbonyl group. Hence dipole-dipole force is present between formaldehyde molecules.Carbon tetrafluoride is a non-polar molecule due to it's symmetrical structure. hence only van der waal force exists between carbon tetrafluoride molecules.Order of intermolecular force (decreasing order): Ionic force > dipole-dipole force > van der waal forceSo ranking of given compounds in order of decreasing boiling point : KF  > Formaldehyde > Carbon tertrafluoride

Nonmetals usually react by gaining electrons

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.