I always wondered when a Prime dies and he passes the Matrix to his successor, does he know that when passing on the Matrix that he is the chosen or not? Like when Optimus was dieing and he passed the Matrix to Ultra Magnus.

It goes down to who Hasbro or Takara wants to be the next prime. That's as far as it goes, a yes or no to a character by them.

I'm going to say no, they do not know if who they pass it on to is the chosen one. Prime passed it to Magnus because he was high in the ranks and an old friend they were very close. Though I assume if Magnus hadn't been there Prime would have passed it to someone like Prowl. Hot Rod wouldn't have been a thought due to his rank and his inexperience.

It's really a grey area, and I don't think it's ever been stated for certain. The matrix holder seems to choose his successor based on who they believe should lead (how Optimus Prime chose Ultra Magnus), and this is something of a political and social succession. However, this choice will not necessarily be a "chosen one" of the Matrix, which is driven by whatever consciousness the matrix seems to possess. Chosen Ones can be from unlikely origins, and can even be from the Decepticons, Chosen by the Matrix to fulfill some important task or role. In many cases, this nigh-supernatural ascension supercedes the previously mentioned political succession. In short, no, I don't think they know who the Matrix wants to hold it.

I think there are Matrix Bearers and Chosen Ones. They're not often the same thing. Was Optimus ever actually a 'Chosen One'? Or was he just a really accomplished Matrix Bearer? How often is a Matrix Bearer called upon to properly 'Light our darkest hour'? Once? Twice? Never? Optimus Prime selected Ultra Magus as a suitable Matrix Bearer. But the Matrix selected Hot Rod as a Chosen One. Most are selected. Few are actually destined.

It didn't matter who Optimus passed the Matrix to. Hot Rod was the Chosen One. The Matrix wouldn't change Kup like it changed Hot Rod. If Optimus had selected Kup as the next Matrix Bearer then Kup wouldn't have been Kupimus Prime. Proof of that is everyone didn't suddenly start calling Ultra Magnus 'Ultra Magnusmus Prime' once he got his hands on the Matrix. And in fact you'll notice the Matrix didn't change Hot Rod the moment he caught the Matrix after Optimus dropped it either. Hot Rod was the Chosen One, changed only at the correct time to Light the Darkest Hour, which was to defeat Unicron and lead after. If Unicron hadn't shown up for another twenty years Hot Rod could've probably handled the Matrix many times during that and still not been changed into Rodimus Prime because it wasn't his 'time' to be the Chosen One. A more interesting question is after Optimus was properly restored to life in Return of Optimus Prime and he got the Matrix back, would Hot Rod change into Rodimus Prime again if he touched the Matrix again after? Was Hot Rod only the Chosen One for the purpose of defeating Unicron and up until Optimus Prime was fully revived? We saw that Rodimus would change back to Hot Rod when the 'zombie' Optimus had the Matrix and that Hot Rod would become Rodimus Prime again when he recovered it, but that was because Optimus was to all intents and purposes still kinda dead and so it was still the Chosen One's destined time to lead. Until we see Hot Rod get changed by the Matrix back into Rodimus Prime while Optimus is still alive and fully functional (and I'm not counting the 'Two Primes' episide of the Japanese series here) it can be assumed that Hot Rod's time as the 'Chosen One' is over. Add in that the Matrix was emptied at the end of Return of Optimus Prime and that could actually have 'reset' it so the connection to Hot Rod as a Chosen One has been severed. There's every likelihood that should Optimus Prime die again a completely different destined Chosen One might be called upon instead of Hot Rod at some point. Optimus could still pass the Matrix to Hot Rod to be a Matrix Bearer after his death, but that doesn't make him Rodimus Prime again. In that respect you could suggest that Hot Rod's time as the Chosen One was only destined for the duration between him defeating Unicron and Optimus being properly restored to life. Hot Rod as the Chosen One was more just a stand-in period. For the purposes of this idea I'm ignoring the time in the comics where Rodimus changed back to Hot Rod in Space Pirates and Optimus was never coming back from the dead in those future tales. This is strictly about the US animations. So don't start a 'thing' about it.

The way I see, Passing of the Matrix is divided into 3 categories: 1, The Matrix Bearer - Prime and UMagnus. The Matrix bearer does not get reformatted or new body. Instead, they get to host the Matrix and can only use the Matrix in a critical situation e.g like Unicron or the Hated Plague. 2, Chosen One - Hot Rod, Scourge. Being chosen by the Matrix mean their body get reformatted as well as the ability to open the Matrix in a critical situation. Young Hot Rod was upgraded into an older body or much mature bot. Scourge who is already old, was upgraded to even more older when he put the Matrix inside him. These bots can go back to their normal self or to their upgraded body as many times as they want regardless of the situation critical or not as long as they retain the Matrix. This example can be seen in the episode Burden Hardest to Bear. 3, The Rejectors, Non-Matrix Bearer, Casual Bots, whatever you want call them - Gavaltron. These unfortunate bots cannot host and is incompatible with the Matrix. If they try to put the Matrix inside them, it will get rejected causing them to feel uncomfortable. Anyhow, that's my 2cents not sure it make sense or not.

Here's the real question: if Ultra Magnus didn't fumble the Matrix, would the Matrix chose him instead? I always thought that the "energy" released when you see Hot Rod catch the Matrix was the Matrix imprinting on it's new holder, kinda like a baby chick thinking that the first thing it sees after hatching is it's mother.

I don't think so. Rodimus was pretty explicitly stated to be the chosen one, built in Primus' own image, so even if he had caught the matrix and shoved it into his chest without incident, the rest of the film would have still played out the way it did.

Its funny that when Prime dropped the matrix and Hot rod caught it, it actually responded to him, but then when passed to Magnus, he couldnt even fit iit into his chest compartment (almost like it was trying to jump out at one point).

if that energy/light show had been noticed/acknowledged by any of the characters in the film then I might see your point here. that display was for the benefit of the viewer only, meaning us, it was a hint as to who the chosen was.