Which of the following is a balanced chemical equation?

2NaOH(aq) + Zn(s) → Na₂ZnO₂(s) + H₂(g)

The correct answer is option 4. 2NaOH(aq) + Zn(s) → Na₂ZnO₂(s) + H₂(g)

In a balanced chemical equation, the number of atoms of each element must be the same on both the reactant and product sides to ensure the conservation of mass.

Let's analyze the given chemical equation:

\[ 2NaOH(aq) + Zn(s) \rightarrow Na_2ZnO_2(s) + H_2(g) \]

On the reactant side:

There are 2 sodium (Na) atoms, 

2 oxygen (O) atoms,

2 hydrogen (H) atoms from the hydroxide (OH) group, and 

1 zinc (Zn) atom.

On the product side:

There are 2 sodium (Na) atoms, 

1 zinc (Zn) atom, 

2 oxygen (O) atoms, and 

2 hydrogen (H) atoms.

By ensuring that the number of atoms of each element is the same on both sides, we can see that the equation is balanced:

Reactant side: 2 Na, 2 O, 2 H, 1 Zn

Product side: 2 Na, 2 O, 2 H, 1 Zn

Therefore, the equation is balanced, and all atoms are accounted for in the reaction.