Metals of very high reactivity are usually extracted from their purified molten ores by which process?

Introduction / Context:
This question focuses on the metallurgical principle used to extract metals that are highly reactive, such as sodium, potassium, calcium, and aluminium. These metals occupy the top part of the reactivity series and have very strong attraction for oxygen and other non metals. Therefore, ordinary chemical reduction methods are not sufficient to free them from their compounds. Understanding which extraction method is suitable for different reactivity levels is a core concept in basic metallurgy.

Given Data / Assumptions:

• The metals are described as being of high reactivity.
• The ores are already purified and in molten form.
• We must choose the process that is realistically used in industry for such metals.
• Available processes are reduction with a chemical reducing agent, roasting, electrolysis, and calcination.

Concept / Approach:
The reactivity series tells us that highly reactive metals form very stable compounds. For those metals, conventional reducing agents like carbon cannot reduce the metal oxide or chloride because carbon is less reactive. Instead, we use electrolysis of molten salts or molten ores, where an electric current directly supplies electrons to metal ions at the cathode. This method is used for metals such as sodium from molten sodium chloride and aluminium from molten aluminium oxide dissolved in cryolite.

Step-by-Step Solution:
Step 1: Identify metals of high reactivity. Examples include K, Na, Ca, Mg, and Al. Step 2: Recall their extraction method. Sodium is obtained by electrolysis of molten sodium chloride. Aluminium is obtained by electrolysis of molten alumina in cryolite (Hall Heroult process). Step 3: Compare with methods given in the options. Reduction by a chemical agent works for less reactive metals like iron and zinc. Roasting and calcination are mainly for converting ores to oxides and for removing volatile impurities, not for extracting highly reactive metals directly. Step 4: Conclude that electrolysis of molten ore is the standard industrial method.

Verification / Alternative Check:
Looking at standard chemistry textbooks, extraction of sodium and potassium is always shown through Down cell electrolysis of molten chlorides. Aluminium extraction is also always linked to the Hall Heroult electrolytic process. None of these processes rely on carbon reduction at high temperature. Therefore the choice of electrolysis is consistent with the well known industrial practice for highly reactive metals.

Why Other Options Are Wrong:
Option A: Reduction by an appropriate reducing agent works for moderately reactive metals such as iron from iron oxide using carbon or carbon monoxide. It is not effective for very reactive metals. Option B: Roasting is heating an ore in the presence of oxygen, usually to convert sulphide ores to oxides. It is a preliminary step, not the final extraction method for highly reactive metals. Option D: Calcination is heating an ore in the absence or limited supply of air to remove moisture or volatile impurities, commonly used for carbonate ores. It again is a preparatory step, not the main extraction technique for very reactive metals.

Common Pitfalls:
A frequent mistake is to think that roasting or calcination always gives the metal itself. In fact, these processes mostly produce oxides which then need further reduction. Another confusion is between extraction of iron, which uses a blast furnace, and extraction of aluminium or sodium, which uses electrolysis. Keeping clear the link between position in the reactivity series and extraction method prevents such confusion.

Final Answer:
Metals of high reactivity are extracted from purified molten ore by Electrolysis.