Which one of the following is not an example of a combination reaction a. 2h2o(> 2h2(g)+o2(g) b. 2k+> 2kci c. 2h2+> 2h2o d. 2mg+> 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. 

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