Which variable is best to use when determining the rate of decomposition of hydrogen peroxide?

$${\text{2}}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}{\text{(l)}} \to {\text{2}}{{\text{H}}_{\text{2}}}{\text{O(l)}} + {{\text{O}}_{\text{2}}}{\text{(g)}}$$

A.     Volume of solution

B.     Volume of gas

C.     pH of solution

D.     Conductivity of solution

B