(a) Number of moles = 2.5 moles

Molar mass of hydrogen peroxides (H₂O₂) = (2 x 1) + (2 x 16) = 2 + 32 = 34 g

Mass of H₂O₂

= number of moles x Molar mass

= 2.5 x 34

= 85 g

(b) Mass of hydrogen peroxides (H₂O₂) = 30 g

Molar mass of hydrogen peroxides (H₂O₂) = (2 x 1) + (2 x 16) = 2 + 32 = 34 g

$\text{Number of moles} = \frac{\text{Mass in grams}}{\text{Molar mass}}$ 

$\text{Number of moles} = \frac{30}{34}$

$\therefore \text{Number of moles} = 0.88 \text{ moles}$