Answer: The molar mass of each gas
Explanation:
Mole fraction is the ratio of moles of that component to the total moles of solution. Moles of solute is the ratio of given mass to the molar mass.

Suppose if there are three gases A, B and C.
a) 
b) 
c) 
moles of solute =
Thus if mass of each gas is known , we must know the molar mass of each gas to know the moles of each gas.
This is Bohrs model for potassium

The chemical property deals with the ability of a substance being able to burn is called combustibility [ option b ] .
<u>More</u><u> to</u><u> know</u><u> </u><u>:</u><u>-</u>
<em>1</em><em>)</em><em> </em><em>Combustion</em><em> </em><em>:</em><em>-</em>
Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives out heat.
The fuel can be any one of the 3 states of matter that is - solid , liquid & gases .
Examples of combustible substances :-
Solid - Coal
Liquid - Petrol , Disel , etc.
Gas - Hydrogen , Oxygen , etc .