How many types of the biological elements are used in living organisms?

Answer 1

Quick answer? Almost all of them. Take a look at the periodic table - if it is not a heavy/rare metal (platinum, palladium, titanium, etc) or an experimental super atom (the higher numbers) then it is likely in use by quite a few living organisms. In the case of the smaller atoms, or the more common elements, such as hydrogen, carbon, and nitrogen, the answer is as close to 100% as you can get - our bioshpere is anchored in carbon-based lifeforms, after all. In general, the higher the atomic number or the larger the atom, the organisms using that particular element will be fewer and farther between.