Question 2
What is the freezing point of water in Celcius

0°C

Explanation:

The freezing point of water is zero (0) degrees Celsius. Converted to Kelvin it is 273.15 kelvin. At these temperatures pure liquid water, and at 1 atm, changes to ice.  The boiling point of water, on the other hand, is 100 degrees Celsius, temperatures at which liquid changes to a gaseous phase (water vapour).

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.