Answer:-
A. A water molecule
Explanation:-
A molecule is the smallest particle of a compound that retains all it's chemical properties.
Here H2O is a compound. So the smallest particle that will retain all the chemical properties and still remain water is water molecule.
Atoms Hydrogen and Oxygen both have different chemical properties from water H2O and are thus different.
Hydrogen peroxide is different molecule from water. So it is also not water.
2, 4, 1
Explanation:
We have the following chemical reaction:
Ag₂O → Ag + O₂
To balance the chemical equation the number of atoms of each element entering the reaction have to be equal to the number of atoms of each element leaving the reaction, in order to conserve the mass.
So the balanced chemical equation is:
2 Ag₂O → 4 Ag + O₂
Learn more about:
balancing chemical equations
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Double replacement because H and K are both switching