They are kind of opposite processes. Chemical synthesis is execution of chemical reactions to make products. Like you take two substances, you put them together, they react and you have new a substance. For example.

here Sodium and Chlorine react to make a new substance which is Sodium Chloride.
Chemical decomposition is process of seperating a substance to different substances. There is a substance by a reaction this substance becomes two substances, Like : XY -> X+Y For example :
Iron because it is formed by metal atoms.
Answer:
B. False
Explanation:
the reaction is
H₂0 + O₂ = H₂O
as addition of oxygen means burning in the system which means heating or energy is necessary for the reactants. SO the reaction is spontaneous and exothermic .
As according to second law of thermodynamics
the change in enthalpy is greater than or equal to zero when the reaction is spontaneous, so enthalpy will increase in the above reaction.
H2 burning in O2 to form H2O (l) is an example of a system where the entropy of the universe increases.