A student measures the pH of pure water at 50∘C and records a value of 7.00. Based on this measurement, the water sample is best described as
a) acidic, because Kw is larger at 50∘C than at 25∘C, so [H3O+]>[OH−] in pure water
b) neutral, because a pH of 7 is defined as neutral regardless of temperature
c) basic, because the pH that corresponds to neutrality at 50∘C is below 7
d) indeterminate, because the pH scale itself changes with temperature, so acidity cannot be classified from pH alone