An unknown gas effuses 0.5 times faster than hydrogen gas (h2). what is the molecular mass of the gas? 1.008 g/mol 4.064 g/mol 2.0 g. mol 8 g/mol

Rate of Effusion of Unknown gas  =  rX  =  0.5

Rate of Effusion of Hydrogen        =  rH  =  1

M.mass of Hydrogen                     = mH  =  2 g/mol

M.mass of Unknown gas              = mX  =  ?

Formula used:

                            rH / rX  = √mX / mH

taking square on both sides,
 
                            r²H / r²X  =  mX / mH
Solving for mX,
                                      mX  = (r²H ÷ r²X) × mH
Putting values,
                                      mX  =  [1² ÷ (0.5)²] × 2 g/mol

                                      mX  =  (1 ÷ 0.25) × 2 g/mol
            
                                      mX  =  4 × 2 g/mol

                                      mX  =  8 g/mol

Result:
           Molecular Mass of Unknown gas is 8 g/mol.

Noble gases is far right