Mass of Li = 237.38 g
The mole itself is the number of particles contained in a substance amounting to 6.02.10²³
[tex]\large {\boxed {\boxed {\bold {mol = \frac {mass} {molar \: mass}}}}[/tex]
Moles of Li = 34.2
Molar mass(MW) of Li = 6.941 g/mol
then mass of Lithium (Li) :
[tex]\tt mol=\dfrac{mass}{MW}\\\\mass=mol\times MW\\\\mass=34.2\times 6,941~g/mol\\\\mass=\boxed{\bold{237.38~g}}[/tex]