In which type of reaction do two or more substances combine to produce a single substance?
(1) synthesis
(2) decomposition
(3) single replacement
(4) double replacement

The correct answer is (1) Synthesis

Explanation:

In chemistry, synthesis reaction occurs as two or more substance combine and form a single and complex product, due to this, synthesis reaction is also known as a direct combination, because different to decomposition or replacement reactions the final product includes the substances that were combined. For example, water (H2O) is formed through synthesis by mixing two atoms of hydrogen (H2) and one of Oxygen (H) which means the substances combined form a single substance. Thus, the type of reaction described is Synthesis reaction.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

c. 75.7

i think that is the right