I think the correct answer from the choices listed above is option A. The fact that we know about the relationship between the hotter water and the cooler water would be that the <span> hotter water is less dense. Hope this answers the question. Have a nice day.</span>
It's decomposition
A combustion reaction involves carbon dioxide so it can't be that
The water is not being formed
The water is not replaced by the other molecules
So it is decomposition, not just from process of elimination, but also because decomposing water means heating it.
I am probably wrong but I would think 900. I wouldn’t submit that without somebody backing me up though.