In industrial fat processing, which gas is commonly used to convert vegetable oils into semi solid vegetable ghee or vanaspati by hydrogenation?

Introduction / Context:
This question relates to applied chemistry and the food industry. Vegetable oils can be chemically changed into semi solid fats called vanaspati or vegetable ghee through a process called hydrogenation. Knowing which gas is used in this process helps connect organic chemistry concepts like addition reactions to everyday food products.

Given Data / Assumptions:
- The process mentioned is making vegetables and vanaspati from vegetable oils, which refers to hydrogenation of unsaturated oils.
- The options list gases: hydrogen, nitrogen, argon and helium.
- We assume a typical industrial process where unsaturated double bonds in fatty acid chains are converted to single bonds.

Concept / Approach:
Vegetable oils are largely composed of triglycerides containing unsaturated fatty acids with carbon carbon double bonds. During hydrogenation, hydrogen gas is passed over the heated oil in the presence of a metal catalyst such as nickel. Hydrogen adds across the double bonds, converting them into single bonds and making the fat more saturated. This increases melting point and turns the liquid oil into a semi solid fat. Inert gases like nitrogen, argon and helium do not participate in the required addition reaction and therefore are not used as the reactive gas in hydrogenation.

Step-by-Step Solution:
Step 1: Recognise that the process of converting liquid vegetable oils into semi solid vanaspati is called hydrogenation. Step 2: Recall that hydrogenation literally means addition of hydrogen across carbon carbon double bonds in unsaturated fatty acid chains. Step 3: Note that hydrogen gas (H2) is the reactive gas that provides the hydrogen atoms needed for this addition reaction. Step 4: Identify that nitrogen, argon and helium are largely inert under these conditions and are not used to saturate double bonds in oils. Step 5: Conclude that hydrogen gas is the correct choice.

Verification / Alternative check:
In organic chemistry, typical hydrogenation reactions are written as RCH=CHR + H2 leading to RCH2 CH2R in the presence of catalysts like Ni, Pt or Pd. Industrial production of margarine and vanaspati uses exactly this type of reaction on large triglyceride molecules. The name "hydrogenated vegetable oil" appears on many food labels, directly indicating hydrogen as the reacting gas. Nitrogen, argon and helium are sometimes used as inert atmospheres in chemical processes but they do not add to double bonds in this context.

Why Other Options Are Wrong:
Nitrogen: Although relatively inert and sometimes used to blanket tanks, nitrogen does not add across double bonds to convert oils into fats.
Argon and Helium: Both are noble gases, chemically inert under normal conditions and unsuitable as reagents for hydrogenation; they are used as protective atmospheres, not as reactive gases.

Common Pitfalls:
A possible misunderstanding is to confuse gases used for inert atmospheres or packaging with gases that actively react in chemical processes. Students may also see the mention of vanaspati and think only of food processing without linking it to the underlying organic reaction. To avoid this, remember that hydrogenation of oils is a classic alkene addition reaction, and hydrogen is the necessary reactant gas.

Final Answer:
The gas used to convert vegetable oils into vanaspati by hydrogenation is hydrogen.