Adouble-replacement reaction, the
a. products are always molecular
b. reactants are two ionic compounds
c. reactants are two elements
d. products are a new element and a new compound

b. reactants are two ionic compounds.

Explanation:

A double-replacement reaction is different from a single-replacement reaction  because a double-replacement reaction is a reaction between two ionic compounds while in a single-replacement reaction one atom replace another atom. In addition, the product formed from a double-replacement reaction often precipitate from the given solution.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

increased stability in the completion of fluorine's outer shell.