Concept:Soluble salts are formed by reactions that leave the salt dissolved in water, whereas double decomposition is used for preparing insoluble salts by precipitation.
Explanation:Neutralization of an acid by a base gives a soluble salt and water.
The reaction of an acid with an electropositive metal produces a soluble salt and hydrogen gas.
The reaction of an acid with a trioxocarbonate(IV) salt yields a soluble salt, water, and carbon dioxide.
Double decomposition involves mixing two solutions to precipitate an insoluble salt, not a soluble salt.
Therefore, double decomposition is not a suitable method for preparing soluble salts.
Answer:C. double decomposition