Which one of the following alcohols undergoes dehydration most easily?

Which fo the following would undergo dehydration most readily?

Which of the following compound undergoes dehydrochlorination most easily when treated with alcoholic KOH-

Which of the following compounds undergoes dehydrohalogenation most easily on heating with alc. KOH?

which of the following compound undergoes dehydrochlorination most easily when treated with alcoholic KOH?