The given equation is
C6H5OH(g)+O2(g)→CO2(g)+H2O(l)
After balanced equation is
C6H5OH(g)+7O2(g)→6CO2(g)+3H2O(l)
Volume of reactant is;
Number of moles of C6H5OH=1
Volume of C6H5OH=30 mL
∴ Moles of Oxygen=7
Volume =7×30=210 mL
Volume of products is ;
Moles of CO2=6
Volume =6×30=180 mL
Moles of H2O=3
Volume =3×30=90 mL
therefore,
∴ Change in volume =Product volume − reactant volume
⇒(180+90)−(210+30)
⇒270−240
⇒30 mL
Hence;
This is the required solution.