Question

Inert atmosphere for welding of metals is obtained by :
(A) $Ar$, $He$
(B) ${N_2}$, $He$
(C) ${O_2}$, ${N_2}$
(D) $Ar$, ${N_2}$

Answer 1

Hint: The inert atmosphere means where the gas does not react with metal and form any different product. All the noble gases are inert. The inertness can be checked from the electronic configuration and bonding. The element with filled electronic configuration is inert and the one having any double or triple bond in molecular form is reactive.

Complete step by step solution:
-Let us first understand the meaning of word inert. The inert means which do not react. Such substances are very stable and do react with any other species. The noble gases in the periodic table have filled orbitals and are thus more stable. These are inert and thus also called inert gases.
-In case of welding of metals, the inert atmosphere will be provided by those gases which do not react with metals.
-Now, let us see the options given to us one by one and find out the correct answer.
-The first gas given is Argon. It is a noble gas and is thus inert.
-The second gas given is Helium. Even helium having atomic number two has $2s$ orbital filled.
-It is also inert.
-The third gas is the nitrogen with molecular formula ${N_2}$. This ${N_2}$ can react with metals forming complexes. Thus, it can not be regarded as inert and is reactive.
-The fourth gas is ${O_2}$. The dioxygen is also reactive. It reacts with metals forming various oxides. So, even this is not the correct answer.
-On seeing the options, the option a.) contains both the inert gases.

Thus, the option (A) is the correct answer.

Note: It must be noted that although the dinitrogen has its valency complete there is a triple bond between two nitrogen atoms and we know that the triple bond is more reactive than single and double bonds. Similar is the case with dioxygen, it consists of a double bond in between two oxygen atoms which can react.