Question

which of the following equations does not follow the law of conservation of mass?
o na + cl---> nacl
o na + cl2--> nacl
o nacl---> na + cl
o all of these follow the law of conservation of mass

Explanation:

Step1: Check the first equation

The first equation $\text{Na}+\text{Cl}
ightarrow\text{NaCl}$ is not balanced as chlorine exists as $\text{Cl}_2$ in its elemental form in nature, but this doesn't directly violate mass - conservation yet.

Step2: Check the second equation

The second equation $\text{Na}+\text{Cl}_2
ightarrow\text{NaCl}$ is unbalanced. On the left - hand side, there are 2 chlorine atoms in $\text{Cl}_2$, but only 1 chlorine atom in $\text{NaCl}$ on the right - hand side. According to the law of conservation of mass, the number of atoms of each element must be the same on both sides of a chemical equation. This equation violates the law of conservation of mass.

Step3: Check the third equation

The third equation $\text{NaCl}
ightarrow\text{Na}+\text{Cl}$ is also not a proper representation as chlorine exists as $\text{Cl}_2$ in elemental form, but again, if we consider it in terms of atoms, it is a decomposition reaction and can be balanced properly in a more correct form.

Answer:

Na + Cl2--> NaCl