The ratio mass of oxygen and nitrogen of a particular gaseowa mixture is ( 1: 4 . ) The ratio of number of their molecule is.
(a) 1: 4
(b) 7: 32
(c) 1: 8
(d) 3: 16

( frac{n_{mathrm{O}_{2}}}{n_{mathrm{N}_{2}}}=frac{left(m_{mathrm{O}_{2}}right)}{frac{left(M_{mathrm{O}_{2}}right)}{left(M_{mathrm{N}_{2}}right)}} )
( =0.9 times 60 mathrm{mg}= )
where, ( m_{mathrm{O}_{2}}= ) given mass of ( mathrm{O}_{2}, m_{mathrm{N}_{2}}= ) given mass of ( mathrm{N}_{2} ) ( M_{mathrm{O}_{2}}= ) molecular mass of ( mathrm{O}_{2}, M_{mathrm{N}_{2}}= ) molecular mass of ( mathrm{N}_{2} )
( n_{mathrm{O}_{2}}= ) number of moles of ( mathrm{O}_{2}, n_{mathrm{N}_{2}}= ) number of moles of ( mathrm{N}_{2} )
[
=left[frac{m_{mathrm{O}_{2}}}{m_{mathrm{N}}} mid frac{28}{32}=frac{1}{4} times frac{28}{32}=frac{7}{32}right.
]