How many moles of acetylene (c2h6) had occupy a volume of 3.25l at stp?

The number of moles of acetylene can be found out using the ideal gas law equation 
PV = nRT
where P - standard pressure - 101 325 Pa
V - volume -  3.25 x 10⁻³ m³
n - number of moles 
R - universal gas constant - 8.314 Jmol⁻¹K⁻¹
T - standard temperature - 273 K
substituting these values in the equation 
101 325 Pa x 3.25 x 10⁻³ m³ = n x 8.314 Jmol⁻¹K⁻¹ x 273 K
n = 0.145 mol
number of moles of acetylene are 0.145 mol

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.