Answer
a. 0.78 mole
b. 1.95 moles
c. 6.0 moles
Work Step by Step
a. Molar mass: 32.06 g/mol $$ 25 \space g \times \frac{1 \space mole}{ 32.06 \space g} = 0.78 \space mole$$
b. Molar mass: ( 16.00 $\times$ 2 )+ ( 32.06 $\times$ 1 )= 64.06 g/mol $$ 125 \space g \times \frac{1 \space mole \space SO_2}{ 64.06 \space g} = 1.95 \space moles \space SO_2$$
Each $SO_2$ has 1 $S$ atom, thus: $$ 1.95 \space mole \space SO_2 \times \frac{1 \space mole \space S}{ 1 \space mole \space SO_2} = 1.95 \space moles \space S$$
c. Each $ Al_2S_3 $ has 3 S atoms, thus:$$ 2.0 \space mole \space Al_2S_3 \times \frac{ 3 \space moles \ S }{1 \space mole \space Al_2S_3 } = 6.0 \space moles \space S $$
