Question

Which of the following turns into gas first and separates from air?
A.Nitrogen
B.Oxygen
C.Argon
D.Helium

Answer 1

Hint:Air is a heterogeneous mixture containing a variety of gases and various solid particles dispersed into it. When liquefied, air is filtered and cooled to a temperature of around $ - 200$ degree Celsius.

Complete answer:
Gases are separated from liquefied air by using the method of fractional distillation. The fractional distillation method of separation of substances is based on the principle of the difference in boiling points of the substances in the mixture. It is generally used for the separation of a mixture containing a large number of elements and compounds together. For example it is used for separation of gases from air and for separation of petrol and its products.
The boiling point of a substance at which it turns into vapours from liquid or into liquid from vapour phase. As a result, during fractional distillation the gas having the lowest boiling point will turn into a gas and distil out separating from the mixture. So the gas with the lowest boiling point among the following will first separate from air.
Liquid nitrogen has a boiling point of $ - 190$ degree Celsius. It turns into a gas first and separates from air.

Thus, the correct answer is A.

Note:
Helium has a lower boiling point than nitrogen. It liquefies at a temperature of around $ - 270$ degree Celsius almost near to absolute zero. Hence, when air is liquefied, helium is not generally present in the liquid mixture. Among the others, nitrogen is the first to separate out followed by Argon and then oxygen.