The coordination number is 6. The outer Cl- ion isn't included, so you count 4 x NH3 and 2 x Cl- are within Co's coordination sphere.
Thomson used a beam of negatively charged particles. Using a beam of particles and detecting the scattering of the particles after they hit gold foil.
Closed system. If the system is not closed, matter or energy can escape from the system. an example of this is if you react magnesium and hydrochloric acid in a open system. The H₂ gas is going to escape making it look like some of the mass disappeared . in that same reaction some in an open system will also loose heat to the surrounding which will make it look like less heat was produced.