Which one of the following is not an example of a combination reaction a. 2H2O (I) - - - > 2H2 (g) + O2 (g) b. 2K+CI2--->2KCI c. 2H2+O2--->2H2O d. 2Mg+O2--->2MgO

The answer would be A.

Combination reaction, otherwise known as synthesis reaction, occurs when two or more substances react and form a single, more complex substance.

A combination reaction looks like this in an equation:

A + B → AB

reactants product

So from two reactants they become one product.

Let's take a look at choice A.

2H₂O (l) → 2H₂ (g) + O₂ (g)

reactant product (s)

Notice that from one substance, it broke down into two substances. So this is not a combination reaction. This is what you call a decomposition reaction.

In a combination reaction, two reactants combine to form one product therefore option A is NOT a combination reaction.