If the molecular weight of glucose-I-phosphate is 260 and its density is 1.5 g/ml. What is the average volume occupied by 1 molecule of this compound?

We get the volume of 1 mole $=\frac{\mathrm{mass}}{\mathrm{density}}$

We know 1 mole$=6.022\times {10}^{23}$  molecules = Avogadro number

$\frac{260}{1.5}\times \frac{1}{6\times {10}^{28}}$

Thus, the average volume occupied by 1 molecule of this compound is $29\times {10}^{-23} \mathrm{ml}$.