H2O question...

Both hydrogen and oxygen are gases. When they bond together, a pair of electrons is shared between each hydrogen atom and the oxygen atom. This reduces the distance between the hydrogen atom and the oxygen atom thereby releasing energy (bonds are formed if the final product has lesser energy than the initial products). Thus, the kinetic energy of both the gases are lost and they come closer to each other. Thus, contraction occurs and as a result water turns out to be a liquid. If further doubts, do ask me..

The chemical bond between the H and O atoms in water is much stronger than the bond between O and H atoms inside the gas molecules. Because the attraction is mush higher, the molecules in water are closer, thus they appear in a liquid form.

Thats a good question, i think that its the reaction of Hydrogen and Oxygen, when the particles meet they react to create the liquid either that or something to do with heat and condensation maybe