Arrange solids, liquids and gases in ascending order of the intermolecular force of attraction.
Gas< liquid<solid
Think of a solid rock, a bottle of water and some vapour from boiling hot water.
Now imagine all of these things made of tiny, vibrating balls. Done? Now imagine these balls trying to pull each other like 2 people holding hands and pulling.
In which one do you think the balls are pulling each other most strongly? The rock right? Yes! It is exactly because these balls (atoms/molecules) are pulling so strongly, the rock is so strong. In water, the balls are moving about more quickly and are more far apart. That's why they are not able to hold each other as strongly. Can you hold your friend who is moving and is far from you? Difficult!
Now imagine the friend is flying away and you had to hold! Almost impossible. That's why gases have balls moving very fast and very far away from each other.
This pulling is what we call intermolecular force of attraction. So gases < liquids < solids.