This answer is not correct. A Grignard reagent will react with an alcohol in an acid-base reaction and form an this case methane, which would bubble out of the solution. The problem with this answer is that the attack of the reagent is on the hydrogen atom attached to the oxygen atom and both alcohols will react. The isopropyl alcohol would react a bit faster due to steric inhibition of the reaction but not enough so that you could make a reasonable decision as to which was which.