___NH3+ __H2SO4 → (NH4)2SO4

a. Decomposition
b. Single Replacement
c. Combustion
d. Synthesis
e. Double Replacement

The answer to your question is letter d. Synthesis

Explanation:

a. In a decomposition reaction, one single reactant splits out and forms 2 or more products.

b. In a single replacement reaction, a single atom replaces the cation of a molecule.

c. In a combustion reaction, an organic molecule reacts with oxygen to form carbon dioxide and water.

d. In a synthesis reaction, two reactants or more reactants combine to form one single product.

e. In a double replacement reaction, two molecules interchange cations and anions.