Why is it reasonable to assume the specific heats of naoh and hcl solutions are the same as water?

It would be reasonable to assume that the specific heats of NaOH and HCl solutions are the same as water given that the concentration of these solutions are low about 1 M or less.  Having low concentrations would mean that there is only small amount of particles of HCl or NaOH in the solution so most of the properties of the solution is the same as that of a pure water since less particles can interfere with any process. Specific heat is the amount of heat energy needed per mass in order to be able to raise the temperature by a degree. So, when these particles are present in small amount, it is only the water that would determine the amount of heat needed.

Exothermic,  physical change after it is already baked