In this reaction a scheme of a chemical reaction. the reactants are two molecules, one of which consists of a and b, and the other consists of c and d. the products are two molecules, one of which consists of a and c, and the other consists of b and d. the energy of molecules ab and cd is higher than the energy of molecules ac and bd.
(a)- the products have been rearranged to form reactants
(b)-the products have less potential energy than the reactants
(c)-cd is a product
(d)-ac is a reactant
(e)-entropy has decreased

The answer to your question is: correct answer is A

Explanation:

Reaction

                  AB   +   CD   ⇒    AC   +   BD

(a)- the products have been rearranged to form reactants  This option is correcrt because it is a double substitution reaction, and the reactants interchange cations and anions to form new compounds.

(b)-the products have less potential energy than the reactants  I think this option is wrong because products have less activation energy than the reactants not potential energy.

(c)-CD is a product  This option is wrong, CD is a reactant

(d)-AC is a reactant  This option is wrong, AC is a product

(e)-entropy has decreased , to know this we the data, and the question do not give enough information about this.

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.