As wavelength increases frequency decreases. how can i explain this using a formula?

Because frequency and wavelength are related by a constant (c) the energy can also be written in terms of wavelength: E = h · c / λ. 

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.