If the oil thickness is 200 nm and the index is 1.5, what (vacuum) wavelength (in nm) does a diver see looking at the same position as the scientist, but from under water?

Your answer is c. explanation: plasma  is the fourth state of matter, derived from the gaseous state of matter.  plasma  can contain free  electrons  and/or  ions. while  plasma is never neutral, it can either be positively or negatively charged.  gases, however, are electrically neutral.