Concept Explanation: Extraction of Highly Reactive Metals

Highly reactive metals such as Sodium (Na), Potassium (K), and Magnesium (Mg) have a strong tendency to lose electrons and form positive ions. They are located at the top of the reactivity series and cannot be reduced by common reducing agents like carbon (C) or aluminium (Al) because their affinity for oxygen is higher. Therefore, these metals are extracted using electrolysis of their molten compounds.

Why Electrolysis?

Electrolysis is the process of decomposing an ionic compound in its molten state (or in solution) by passing an electric current. For highly reactive metals:

• They cannot be reduced by chemical reducing agents due to their high reactivity.
• Their compounds (like chlorides or oxides) are stable and require strong energy to break the ionic bonds.
• Electrolysis provides the necessary energy to reduce the metal ions to metal atoms.

Step-by-Step Reasoning for the Given Options:

Step 1: Evaluate "electrolysis of their molten oxides" – While possible, oxides of these metals have very high melting points, making the process energy-intensive and less efficient. For example, magnesium oxide (MgO) melts at about 2800°C.

Step 2: Evaluate "reduction by aluminium" – Aluminium is a good reducing agent for metals below it in the reactivity series (e.g., chromium, manganese), but not for metals above it like Na, K, Mg.

Step 3: Evaluate "reduction by carbon" – Carbon reduction works for metals like zinc, iron, and lead, which are moderately reactive. However, for highly reactive metals, the carbides formed (e.g., sodium carbide) are unstable or not feasible.

Step 4: Evaluate "electrolysis of their molten chloride" – This is the most common and practical method. Chlorides of these metals have lower melting points compared to oxides. For instance, sodium chloride (NaCl) melts at 801°C, and electrolysis of molten NaCl produces sodium metal at the cathode and chlorine gas at the anode.

Final Answer: The correct method is electrolysis of their molten chloride.

Related Topics:

• Reactivity Series of Metals
• Electrolytic Reduction
• Extraction of Metals (e.g., Aluminium, Copper)
• Electrolysis Principles

Formulae and Theory:

Electrolysis of Molten Sodium Chloride:

At cathode (reduction): ${\mathrm{Na}}^{+}+e^{-}\to \mathrm{Na}$

At anode (oxidation): $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2+2e^{-}$

Overall Reaction: $$\begin{gathered} 2\mathrm{NaCl}\left(l\right) \\ \to \\ 2\mathrm{Na}\left(l\right)+{\mathrm{Cl}}_2\left(g\right) \end{gathered}$$

Note: The melting point of NaCl is 801°C, while that of Na₂O is over 1200°C, making chloride electrolysis more efficient.