Question

Argon is used in arc welding because of its
A. low reactivity with metal
B. ability to lower the melting point of metal
C. flammability
D. high calorific value

Answer 1

Hint:Argon is a noble gas and is chemically unreactive. During welding, it is desirable that there is no chemical change. But at high temperatures, the metals react with atmospheric oxygen to form oxides. For this purpose, you should provide an inert atmosphere so that there is no contact between metal and oxygen, and there is no reaction.

Complete answer:
Argon does not have the ability to lower the melting point of metal.
Argon gas is not flammable. Hydrogen gas has high calorific value whereas argon gas has low calorific value.
Hence, you can rule out the options (B) to (D).
The atomic number of argon is 18. It has 18 electrons. K, L and M shells contain 2,8,8 electrons respectively. The valence shell contains 8 electrons. Thus, argon has completed its octet and is highly stable. Usually, argon does not form compounds. So, it is chemically unreactive inert gas, also called noble gas. Thus there is no reaction between argon and the metal to be wielded. Due to low reactivity of argon, during welding, argon can be used to create an inert gas shield. You can blend argon with carbon dioxide gas, hydrogen gas, helium gas or oxygen gas to increase the characteristic properties of arc or to facilitate the transfer of metal in the Gas Metal Arc Welding. Argon is used in arc welding because of its low reactivity with metal.

Hence, the correct option is the option (A).

Note:
During welding you join two metal surfaces. For this purpose, you melt two metal surfaces by heating to a temperature equal to the melting point. For this purpose, you can use an electric arc or oxy-acetylene flame as a heating source.