The correct answers are A and C.
Cooling a substance causes molecules to slow down and get slightly closer together, occupying a smaller volume that results in an increase in density. ... Cold water is more dense and will sink in room-temperature water.
Answer:
>
> 
Explanation:
The order of boiling point depends upon the type of interactions present between the molecules.
Potassium fluoride (KF) is an ionic compound and the opposite ions are held together by strong electrostatic forces.
is a covalent compound and the molecules are held together by weak van der Waals' forces.
Formaldehyde is a polar compound due to presence of polar carbonyl group. Hence dipole-dipole force is present between formaldehyde molecules.
Thus the decreasing order of boiling point is:
>
> 