[humanjoj27]

Hello everyone,,
my teacher just got a question in the world wide web and changed it from 0.355 to 0.255

An unknown gas composed of homonuclear diatomic molecules effuses at a rate that in only 0.255 times that of O2 at the same temperature. what is the identity of unknown gas.

rx/rO2 = sqr mO2/M
rx = 0.255 x rO2

rx/rO2 = 0.255 = sqr 32.0g/mol / mx

solving for uknown molar mass
Mx :
32.0g/mol / mx = (0.255)^2 = 0.065025

Mx = 32.0g/mol / 0.065025 = 492.11 g / mol which is ? gas and cant find it on internet.

[AWK]

Use correctly Graham's Law

https://wiki2.org/en/Graham%27s_law

[MNIO]

via Graham's law
  (rate1 / rate2) = √(mw2 / mw1)

doing a bit of algebra
  (rate1 / rate2)² = mw2 / mw1
  mw2 = mw1 * (rate1 / rate2)²

the original 0.355 gives
  mw2 = 32.00g/mole * (rate1 / 0.355*rate1)² = 254 g/mol

your new # yields
  mw2 = 32.00g/mole * (rate1 / 0.255*rate1)² = 492 g/mol

*********
if you're instructor simply pinched a problem off the internet and changed 0.355 to 0.255, then there is no reason to assume you'll be able to find a real gas with that molar mass.

[AWK]

Even the textbook idea with a 0.355 ratio is suspicious. Iodine boils at a temperature above 180°C.
But the inverse of 1/0.255 gives MW close to the molecular weight of hydrogen. Probably your teacher was thinking about it.