Where, #D# = density of gas = #10.3# g/L #P# = Pressure of gas =#6.43# atm #M# = Molar mass of gas =#39.948# grams/mole #R# = Gas Law constant = #0.0821# Latm/mol K #T# = Temperature of gas =?
#10.3 = (6.43xx39.948)/(0.0821 xx T)#
or, T = 303.76K = #30.61C#
Note: #0K = -273.15#C so subtract this value from the Kelvin value got above to get Celsius value