Why are the elements take part in bonding​

Atoms form chemical bonds to make their outer electron shells more stable. The type of chemical bond maximizes the stability of the atoms that form it. ... Covalent bonds form when sharing atoms results in the highest stability. Other types of bonds besides ionic and covalent chemical bonds exist, too.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.