FTP, name this toxic metalloid with atomic number 33.
It can be detected and quantitated using the Marsh test, which involves reduction by zinc and reaction with hydrogen to form a gas that can be decomposed to give this element in pure form.  With copper, it forms a number of brilliant green compounds such as Scheele Green and Paris Green; these compounds have also found use as insecticides.  In combination with gallium, it forms a direct bandgap semiconductor material used in high frequency applications and semiconductor lasers.  While it has found use in medicine for centuries, including Paul Erlich's "magic bullet" for syphilis, its chemical similarity to phosphorus makes it an allosteric inhibitor of many enzymes, making it and most of its compounds poisonous.  FTP, name this toxic metalloid with atomic number 33.
It can be detected and quantitated using the Marsh test, which involves reduction by zinc and reaction with hydrogen to form a gas that can be decomposed to give this element in pure form.  
arsenic