What type of hybridisation exists in the central atom of ${\mathrm{BCl}}_3$ molecule?

Find out the total number of electrons in a water molecule.

What is the shape of ${\mathrm{BCl}}_3$ molecule?

What is the bond angle between $\mathrm{O}-\mathrm{H}$ bonds of a water molecule?

What type of hybridisation takes place in carbon atom for the formation of graphite? 

Between sigma and pi-bond, which bond is weaker? 

How do you account for the fact that ${\mathrm{H}}_2\mathrm{O}$ is a liquid and ${\mathrm{H}}_2\mathrm{S}$ is a gas at room temperature?