Polar molecules are often able to dissolve in water because
a. the partially charged regions of polar molecules are able to form hydrogen bonds with water molecules.
b. the polar molecules repel each other, allowing them to interact with the water molecules.
c. the polar molecules attract each other, allowing water molecules to adsorb to them.
d. polar molecules are able to fill their valence shells by transferring electrons from water molecules.

a). The partially charged regions of polar molecules are able to form hydrogen

Explanation:

 Polar molecules :

       Those molecules in which positive and negative charge are distributed in random order or unevenly.

The shape of bond between hydrogen and oxygen atoms in water is bend shape that is why water act as polar molecule.It means that most positive charge collect on the hydrogen molecule and most of negative charge will collect on oxygen molecule.

So the our option a is correct.

a). The partially charged regions of polar molecules are able to form hydrogen

c is the answer because when something is left after something evaporates that shows the chemical change.

the answer for sodium is 0.186

the answer for rubidium is 0.251