21) In which list are the ions arranged in order of decreasing size? a) S-2, Br-, K+, Ca+2 b) Br-, S-2, K+, Ca+2 c) K+, Ca+2, S-?, Br- d) Ca+2, K+, S-2, Br-

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.

the answer would be a