yes, actually. it's just a spear with three heads instead of one.
depends on the flail - the historically-odd-yet-classic style one handed flail, no. the more historically accurate peasant's flail? there's...an argument there. they certainly have long enough shafts, but i don't really know what the flail part would be in terms of being attached.
again - yes, actually. it's just a spear meant for throwing.
okay, first off - that's not what an "arm" is. an "arm" is just a weapon. a quarterstaff is a weapon, and thus an arm, as is a spear and even a sword or gun. second - i assume when you say "arm" you mean the "main fighting piece" i was referring to that was in the only actual solid definition of a polearm i could find. okay, that's fine...spears have that. it's the spearhead. javelins also have that, as do tridents. and thirdly - you know a pike is just an extremely long spear, right? that's literally all it is. by including pikes in this list, you have tacitly admitted spears are polearms.