In which form does atom exist in aqueous solution? Give examples.

Atoms are basic unit of mater. They are in the same form in all the states of matter i.e. solid, liquid and gas.

The difference is that in solids, atoms are held closely together by strong atomic interactions. 

Diagramatic representation for solids: circles represent atoms. 

In case of liquids, these atomic interactions are weaker than those in solid form but stronger than the interactions in gases. So, in liquids, the atoms are not as closely packed as they are in solids.

In gases, the atoms are held by very weak interactions, so they are very far from each other.