SSC CGL 2024 Tier-I · 25 September 2024, Shift 3 · General Awareness · Question 10 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

Which of the following gases plays an important role in welding titanium, aluminium, stainless steel, and magnesium?

(a)Fluorine
(b)Chlorine
(c)Argon
(d)Neon

Answer

Why

Correct — C. Welding titanium, aluminium, magnesium and stainless steel needs a gas that will not react with hot metal, and argon is a noble gas — chemically inert.

It is fed over the arc as a shielding gas in TIG and MIG welding, displacing atmospheric oxygen and nitrogen from the molten pool so the weld neither oxidises nor takes up nitrogen and turns brittle.

Argon is also the cheapest inert gas to obtain, making up about 0.93% of the atmosphere, so option (c) is right both chemically and industrially.

Why the others are wrong

(a)
Fluorine — Fluorine is the most reactive non-metal there is. It would attack the workpiece, the electrode and the torch rather than shield anything.
(b)
Chlorine — Chlorine is a reactive halogen used for disinfection and bleaching. Reactivity is precisely the property a shielding gas must not have.
(d)
Neon — Neon is inert like argon, but it is far scarcer in the atmosphere and correspondingly expensive, so its industrial use is discharge lighting rather than welding.

Concept

Molten metal is chemically hungry. At welding temperatures it will pull oxygen and nitrogen straight out of the air, producing oxide inclusions and brittle nitrides in the finished joint.

A shielding gas solves this by physically covering the arc and the pool with something that will not react. Reactive metals — titanium, aluminium, magnesium — need this most, because their oxides form instantly.

Argon is the standard choice: it is a noble gas with a full outer shell, it is denser than air so it stays over the weld, and it is abundant enough to be cheap.

The word doing all the work in this question is 'inert'. Two of the options are halogens, among the most reactive elements known, and two are noble gases. Between the two noble gases, abundance and cost decide.

Key facts

Argon makes up about 0.93% of the Earth's atmosphere by volume, the third most abundant gas after nitrogen and oxygen.
Argon's symbol is Ar and its atomic number is 18.
A shielding gas keeps atmospheric oxygen and nitrogen away from the molten weld pool.
TIG welding is also called gas tungsten arc welding.

Study next

The noble gases and their industrial uses, from helium to radonWhy reactive metals need inert-atmosphere processingComposition of the atmosphere by volume

Common traps

Choosing neon because it is the noble gas students name first, when inertness alone does not decide it.
Assuming a reactive gas such as chlorine would clean or flux the weld.

Noble gases are asked by property rather than by name. Neon and its red glow in a discharge tube come up at 12 Sep 2024, 12:30, GA Q.21, and helium as a monoatomic molecule at 18 Sep 2024, 16:00, GA Q.1.

Related PYQs

No directly related past PYQ was found.