A pokemon cannot evolve or mega evolve in a battle
Depends on which Mega Evolution Charizard has. If X then Charizard because it has high Attack and is a bit more resistant to some of Dragonite's moves such as Aqua Tail and Ice Beam. If Y then probably Dragonite since it has access to Rain Dance, Hurricane, and Thunder.
Neither, by the first posts rules, so it's almost certainly a win for dragonite. Also as a note, both Zards are equally resistant to Ice Beam, being neutral. (& because of drought basically equally resistant to water but not really)
If it were Zard-X, it would depend on movesets (assuming Dragonite has multiscale, otherwise Dragonite just dies lmao). If both have outrage, Zard outspeeds and wins, but outrage is rare. With Dragon Claw, assuming both are 252+ Atk and 0/4 Def, Dragonite is 2HKOd, but has a 37.5% chance of OHKOing Zard, or guaranteed with any sort of power boosting item. If Dragonite has Dragon Dance and Zard does not, dragonite can use DD first to outspeed Zard and OHKO the next turn. They're basically pretty evenly matched, but Zard tends to win if the movesets are mirrored. Zard-Y just flops over and dies because none of its special attacks do much at all and Dragon Claw 2HKOs.