Some elements have variable valancis. why​

because of the different electronic configurations.

I hope this helps

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.

it should be all of them because it asks if you included all of those in your answer

explanation: