Solid thorium(IV) fluoride has a boiling point of 1680C. What is the density of a sample of gaseous thorium(IV)

Solid thorium(IV) fluoride has a boiling point of 1680C. What is the density of a sample of gaseous thorium(IV) fluoride at its boiling point under a pressure of 2.5 atm in a 1.7-L container? Which gas will effuse faster at 1680C, thorium(IV) fluoride or uranium(III) fluoride? How much faster?