10g of helium (mm=4.0g/mol) occupies a volume of 73l at a temperature of 233k. calculate the pressure of this gas

PV = nRT   (where P = pressure; V = volume; n = number of moles; R = gas constant; T = Temperature)
Moles of He = mass of He ÷ molar mass of He                    =  10 g ÷ 4 g/mol                    =  2.5 mol

Now, based on the formula above     P = (nRT) ÷ V
    P = (2.5 mol × (0.082 L · atm/mol · K) × 233 K) ÷  73 L        ≈  0.65 atm

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.