Select the equations that are correctly balanced.
h2o + 2o2 → h2o2
fe2o3 + 3h2 → 2fe + 3h2o
al + 3br2 → albr3
caco3 → cao + co2

Second and Fourth equations

Explanation:

To identify a balanced chemical equation, all you need to do is to compare the number of moles of atoms of each elements in both the reactant and product side of the reactant. If the number of moles of atoms are the same for all elements, it means that the equation is balanced.

First Option;

H2O + 2O2 → H2O2

The two elements present are; Hydrogen (H) and Oxygen (O)

Number of moles of Hydrogen atoms;

Reactant Side = 2, Product Side = 2

Number of moles of Oxygen atoms;

Reactant Side = 4, Product Side = 2

Since the number of moles of oxygen is not balanced in the product side, it means the overall equation is not balanced.

Second Option;

Fe2O3 + 3H2 → 2Fe + 3H2O

The three elements present are; Iron(Fe), Hydrogen (H) and Oxygen (O)

Number of moles of Iron atoms;

Reactant Side = 2, Product Side = 2

Number of moles of Hydrogen atoms;

Reactant Side = 6, Product Side = 6

Number of moles of Oxygen atoms;

Reactant Side = 3, Product Side = 3

Since all the atoms are balanced in both the reactant and product side, the overall equation is balanced.

Third Option;

Al + 3Br2 → AlBr3

The two elements present are; Aluminum (Al) and Bromine (Br)

Number of moles of Aluminum atoms;

Reactant Side = 1, Product Side = 1

Number of moles of Bromine atoms;

Reactant Side = 6, Product Side = 3

Since the number of moles of Bromine is not balanced in the product side, it means the overall equation is not balanced.

Fourth Option;

CaCO3 → CaO + CO2

The three elements present are; Calcium (Ca), Carbon (C) and Oxygen (O)

Number of moles of Calcium atoms;

Reactant Side = 1, Product Side = 1

Number of moles of Carbon atoms;

Reactant Side = 1, Product Side = 1

Number of moles of Oxygen atoms;

Reactant Side = 3, Product Side = (1+2) = 3

Since all the atoms are balanced in both the reactant and product side, the overall equation is balanced.