The pH of a solution is 7. The concentration of hydronium ions in the solution is .

c is the answer because when something is left after something evaporates that shows the chemical change.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.