Which equation is balanced?
o mg + o2 + 2mgo
o2a1+f2 + 2a1f3
o2a1+302 a1,03
o2na+ f2 + 2naf

D) is a balanced chemical equation.

Explanation:

A)

is Unbalanced

The balanced chemical equation will be

B)

is Unbalanced

The balanced chemical equation will be

C)

is Unbalanced

The balanced chemical equation will be

D)

is a balanced chemical equation  

Balancing is making the number of atoms of each element same on both the sides  (reactant and product side).

To find the number of atoms of each element we multiply coefficient and the subscript  

For example  

5 contains  

5 × 1 = 5 ,Ca atoms and

5 × 2 = 10, Cl atoms  

If there is a bracket in the chemical formula  

For example we multiply coefficient × subscript × number outside the bracket to find the number of atoms  

(Please note: 3 is the coefficient, and if there is no number given then 1 will be the coefficient )

So

3 × 3 = 9 , Ca atoms  

3 × 1 × 2 = 6, P atoms  

3 × 4 × 2 = 24, O atoms are present.