Answer:
The 3rd equation.
Cl2 + 2NaBr —> 2NaCl + Br2
Step-by-step explanation:
The law of conservation of matter (mass) states that matter can neither be created nor destroyed during a chemical reaction but can be transferred from one form to another. This implies that unbalanced chemical equation shows that matter (mass) has been created or destroyed.
Now, we shall determine which equation is balanced as follow:
1. 2Cl2 + NaBr —> 2NaCl + Br2
Reactant >>>>>>>> Product
4 Cl >>>>>>>>>>>> 2 Cl
1 Na >>>>>>>>>>>> 2 Na
1 Br >>>>>>>>>>>> 2 Br
Thus, the equation is not balanced.
2. Cl2 + NaBr —> NaCl + Br2
Reactant >>>>>>>> Product
2 Cl >>>>>>>>>>>> 1 Cl
1 Na >>>>>>>>>>>> 1 Na
1 Br >>>>>>>>>>>> 2 Br
Thus, the equation is not balanced.
3. Cl2 + 2NaBr —> 2NaCl + Br2
Reactant >>>>>>>> Product
2 Cl >>>>>>>>>>>> 2 Cl
2 Na >>>>>>>>>>> 2 Na
2 Br >>>>>>>>>>>> 2 Br
Thus, the equation is balanced.
From the illustration made above only the 3rd equation is balanced. And this is in line with the law of the Conservation of matter (mass) as matter (mass) was not created nor destroyed during the chemical reaction but was transferred to other forms.