How many moles are there in 120 g of glucose?

Well, glucose, ${C}_{6} {H}_{12} {O}_{6}$ has a molar mass of $120.16 \cdot g \cdot m o {l}^{-} 1$.
And thus $\text{no. of moles}$ $=$ $\text{Mass"/"Molar mass}$ $=$
$\frac{120 \cdot g}{180.16 \cdot g \cdot m o {l}^{-} 1}$ $\cong$ $\frac{4}{6} \cdot m o l$