How many chemical elements are there, total?
It is hard to say. The number is somewhere in the vicinity of 117, but all of the highest numbered ones are problematic to establish as they tend to decay very quickly. The highest numbered one available in commercial quantities is curium, 96. Since technetium and promethium have no stable isotopes, the number of useful elements can be taken as 94.
The answer is 117 (sort of). The following should clear up the issue: The heaviest element known has an atomic number of 118, which is why some people think this is the answer. But there is a gap, because element 117 has not been discovered yet. Detection of elements 113 and 115 have been reported in scientific journals, but have not yet been officially ratified by IUPAC (the organization responsible for recognizing elements). However, their ratification in the near future is a pretty safe bet. So depending on how you count, the answer is either 115 or 117.
