An element's atomic number is 77. how many electrons would an atom of this element have?

This is known as the element IR. (Iridium) Iridium has the atomic number of 77 therefore has "77 protons, 77 electrons, and 116 neutrons." You can figure out how many protons and electrons a element has by looking at the atomic number. In this case the atomic number is 77 therefore it will have 77 protons and electrons!

Hope this helps! 

Tolerance to high levels of salinity