Mass of H₂O₂ = 88.778 g
The mole itself is the number of particles contained in a substance amounting to 6.02.10²³
Mole can also be determined if the amount of substance mass and its molar mass is known
[tex]\large {\boxed {\boxed {\bold {mol = \frac {mass} {molar \: mass}}}}[/tex]
moles of H₂O₂ = 2.61
So the mass of H₂O₂(MW=34,0147 g/mol) :
[tex]\tt mass=mol\times MW\\\\mass=2.61\times 34,0147 g/mol\\\\mass=88.778~g[/tex]