Final answer:
The neutral metal sphere touched by a positively charged plate gains a positive charge. For the sphere experiment, after touching, each sphere ends up with a charge of −4 nC, which is half of the total initial combined charge.
Step-by-step explanation:
When Orianna touches a positively charged metal plate to a neutral metal sphere, the charge of the metal sphere changes by gaining an excess of positive charge, due to electrons moving from the sphere to the positively charged plate until the potential is equalized. The correct answer to how the charge of the metal sphere changes after touching the positively charged metal plate is A) It gains an excess of positive charge.
In the case of the two charged metal conducting spheres, Sphere A with a charge of −5 nC and Sphere B with a charge of −3 nC, upon touching each other, the charges will redistribute evenly. This is because the spheres are conductors and charges can move freely to achieve equilibrium. Initially, the total combined charge is −8 nC. When the spheres are separated after touching, each sphere will have half of this total charge. Therefore, each sphere will have a charge of −4 nC after they are separated.