All of these are compounds except oxygen because a compound is two or more different elements bonded together.
The chemicals are reactive with one another
The products will be 
<h3>Chemical reactions</h3>
Zn is higher than hydrogen in the reactivity series. Thus, it will be able to displace hydrogen from the acid.
The equation of the reaction becomes: 
Hydrogen gas is released as a result. In fact, it is one of the ways of preparing hydrogen gas in the laboratory.
More on chemical reactivity can be found here: brainly.com/question/9621716
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<span>The choices are as follows:
h2o + 2o2 = h2o2
fe2o3 + 3h2 = 2fe + 3h2o
al + 3br2 = albr3
caco3 = </span><span>cao + co2
The correct answers would be the second and the last option. The equations that are correctly balanced are:
</span> fe2o3 + 3h2 = 2fe + 3h2o
caco3 = cao + co2
To balance, it should be that the number of atoms of each element in the reactant and the product side is equal.
you will use methyl orange to check the pH of a coloured solution
hope it helps
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