If we use molten NaCl , the products of electrolysis are______.

The correct answer is option 4. Sodium metal and \(Cl_2\) gas.

When molten \(NaCl\) is electrolyzed, it breaks down into its constituent ions, sodium ions (\(Na^+\)) and chloride ions (\(Cl^-\)). This process is due to the high temperature of the molten salt, which allows the ions to move freely.

At the cathode (negative electrode), the positively charged sodium ions (\(Na^+\)) are attracted and gain electrons to form sodium atoms (\(Na\)):

\[2Na^+ + 2e^- \rightarrow 2Na\]

At the anode (positive electrode), the negatively charged chloride ions (\(Cl^-\)) lose electrons and undergo oxidation to form chlorine gas (\(Cl_2\)):

\[2Cl^- \rightarrow Cl_2 + 2e^-\]

So, the overall reaction is:

\[2NaCl(l) \rightarrow 2Na(l) + Cl_2(g)\]

Therefore, the products of electrolysis of molten \(NaCl\) are sodium metal (\(Na\)) formed at the cathode and chlorine gas (\(Cl_2\)) formed at the anode. This makes option 4 the correct choice.