UPSEE Solved Model Paper 7

Given:
Ratio of masses of oxygen and nitrogen in a gaseous mixture = 1 : 4
We have to find the ratio of their number of molecules.
Let the mass of oxygen in gaseous mixture be x
Thus, the mass of nitrogen in gaseous mixture = 4x
Now, Number of moles is given as:
Number of moles =

Mass

Molecular‌mass

... (i)
Molecular mass of oxygen = 32
Molecular mass of nitrogen = 28
Substituting the values in equation (i), we get
Number of moles of oxygen =

x

32

... (ii)
Number of moles of nitrogen =

4x

28

... (iii)
Dividing equation (ii) by equation (iii), we get
7 : 32