Calculate the molecular weight of a gas which diffuses four times as fast as another gas `Y`, which in turn diffuses twice as fast as another gas `Z` [All under identical conditions]. Molecules weight of `Z` is `128`.

Explanation

`r_(y)=2r_(z)`
`(r_(y))/(r_(z))=(2r_(z))/(r_(z))=sqrt((128)/(M_(y)))`
`4r_(y)=(128)/(4)=32`
`r_(x)=4r_(y)`
`(r_(x))/(r_(y))=(4r_(y))/(r_(y))=sqrt((32)/(M_(x)))`
`M_(x)=2`