Answer 1:
Instruction 7 and 13 seem to be most difficult for a bot.
7 because it requires a force from thumb and middle affectors that is not so less that the pen falls down and also not so much that the pen does not rotate.
13 because "move" function in itself is a very complex task requiring a lot of force balancing.
Answer 2:
Explicit knowledge in this case are the instructions and intialisations that are feeded to the bot.
Implicit knowledge is the magnitude and direction of forces and torques that are learnt while balancing and rotating the pen during the course of trying to successfully complete all the instructions. This learning of equilibiriums may vary from bot to bot even when same kind of sensors are used, and also frictional values play a critical role.
Chunks can be seen as instructions in this case. Each instruction has its own set of learnt parameters. So, this learning needs to be stored in chunks so that it is easy to recollect. Just like the waiter remembers all the orders after grouping them into "people" who have ordered them in clockwise order. And thus, one obvious grouping is in form of "instructions" which also have an explicit order.
Answer 3:
The firefighter initially tries to implement all his ideas that he thinks can work. Based on whether they work out(rewarded), rules are learnt. With experience, one directly uses these set of rules to extinguish the fire. But initially these rules have to learnt based on reward mechanism(hit and trial).
Simply put, reward mechanism is the way babies figure out that its perhaps not such a good idea to play with fire.