Passage III
When t-butyl chloride [(CH3)3CCI] is dissolved in an acetone-H2O solution, it reacts with H2O completely to form t-butyl alcohol [(CH3)3COH]:
(CH3)3CCI + H2O 
(CH3)3COH + H+ + CI-
Acetone is less polar than H2O. Thus, increasing the concentration of acetone in H2O decreases the polarity of the reaction solution.
Figures 1 and 2 show how the electrical conductivity of each of 5 acetone-H2O solutions varied over time after 1 mg of (CH3)3CCI was dissolved in 100 ml of each solution. The conductivity (which increased as the solution's ion concentration increased) stopped increasing when the reaction had run to completion (indicated by the point labeled "RC").
Figures adapted from Peter Keusch, "Kinetics: Hydrolysis of Tertiary Butyl Halides - First Order Reaction." ©2000 by Universitàt Regensburg.
13. Based on Figures 1 and 2, the reaction was completed soonest when the acetone concentration was:
Your Answer is
Correct Answer is A
Explanation
As can be seen from figure 1, 10% acetone is the first to complete the reaction, and the abscissa of the RC point is about 340 sec