Product
Explanation:
Water in this reaction is called the product of the reaction. 
The product is the new kind of matter formed as a result of a chemical change. They are produced from the combination of reactants. 
                           2H₂  +   O₂        →        2H₂O
                            Reactants              Products 
A chemical reaction involves the combination of chemical species to form a product. The type of reaction above is a called synthesis reaction. 
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The volume did not change, it remained at 20 ml
<h3>Further explanation</h3>
Given
20 ml a sample gas at STP(273 K, 1 atm)
T₂=546 K
P₂=2 atm
Required
The volume
Solution
Combined gas Law :

Input the value :

The volume does not change because the pressure and temperature are increased by the same ratio as the initial conditions (to 2x)