Question

which equation is balanced?
○ na + f₂ → 2naf
○ al + 3o₂ → al₂o₃
○ mg + 2o₂ → 2mgo
○ 2al + 3f₂ → 2alf₃

Explanation:

Step1: Count atoms on reactant side

• $\text{Al}$: $2$ atoms.
• $\text{F}$: $3\times2 = 6$ atoms.

Step2: Count atoms on product side

• $\text{Al}$: $2$ atoms.
• $\text{F}$: $2\times3 = 6$ atoms.

Since the number of $\text{Al}$ and $\text{F}$ atoms is the same on both sides, the equation $2\text{Al} + 3\text{F}_2 \to 2\text{AlF}_3$ is balanced.

For the first option $\text{Na}+\text{F}_2\to 2\text{NaF}$:

Step1: Count atoms on reactant side

• $\text{Na}$: $1$ atom.
• $\text{F}$: $2$ atoms.

Step2: Count atoms on product side

• $\text{Na}$: $2$ atoms.
• $\text{F}$: $2$ atoms.

$\text{Na}$ atoms are not balanced.

For the second option $\text{Al}+3\text{O}_2\to\text{Al}_2\text{O}_3$:

Step1: Count atoms on reactant side

• $\text{Al}$: $1$ atom.
• $\text{O}$: $3\times2 = 6$ atoms.

Step2: Count atoms on product side

• $\text{Al}$: $2$ atoms.
• $\text{O}$: $3$ atoms.

Both $\text{Al}$ and $\text{O}$ atoms are not balanced.

For the third option $\text{Mg}+2\text{O}_2\to 2\text{MgO}$:

Step1: Count atoms on reactant side

• $\text{Mg}$: $1$ atom.
• $\text{O}$: $2\times2 = 4$ atoms.

Step2: Count atoms on product side

• $\text{Mg}$: $2$ atoms.
• $\text{O}$: $2$ atoms.

Both $\text{Mg}$ and $\text{O}$ atoms are not balanced.

Answer:

$2\text{Al} + 3\text{F}_2 \to 2\text{AlF}_3$