Are they Balanced? No.
ASI: +2, +2, -1. That's an odd combination, since penalties to ability scores are very rare in 5E, and is definitely set up to favor Fighters. It is on the high end of the accepted range, making it fine by itself.
Age: Kind of ridiculous since any universe that includes Quazels is automatically at least twenty times as old as the real universe. For reference, reality is approximately 13,772,000,000 years old.
Size: 4'4" and 112 pounds (ignoring the 338 pounds of natural armor) is really big for Small size. Recommend changing this to Medium, with the same reasoning as Dwarf.
Speed: 30' for a Small race is quick. For a Medium race it would be fine.
Heavy Natural Armor: So AC is 18, regardless of equipment, unless that equipment would be better. This is incredibly powerful, overrides a number of class features, and would be sufficient special abilities to make Quaxels a desirable race for fighters and barbarians all by itself.
As several comments noted, this ability needs to be clarified if it is an Unarmored AC.
Change Appearance: Why would the race need to "revert"? That implies that appearance changed in the first place. But there is no ability to change appearance. This ability does nothing, as written.
If it works as implied, granting the race alter self for no spell slots and at will then it is an incredibly powerful racial infiltration ability. As the race's sole feature this would be sufficient to be worth playing. But wait, there's more.
Acid Resistance: Misnamed, since this grants immunity and not resistance. Damage immunity is too powerful for a racial ability.
Acid Breath: A 10' Cone of d8 damage is really weak. And the progression is way too slow. Too weak to be worthwhile, though one more straw on this camel's broken back.
Frightful Appearance: Good ability. Some positives, equivalent negatives. In general, this one is power neutral, though highly desirable for certain character types and play styles.
Languages: A player race that doesn't get Common! That's a bad idea. Bad, bad, bad idea. Characters need to be able to communicate with each other and forcing the Tiefling character to be translator for the Quaxel is going to cause hurt feelings and unneeded tension among the players. Which isn't fun.
Monster Origin: So, you're not a Person for spell targeting. That's a power boost.
Conclusion: Way, way too powerful. Also, too confusing.
Heavy Natural Armor and Change Appearance both need lengthy rewrites and clarifications before they can be playable. The implied effects are individually good enough to be an interesting and powerful race - having both is like getting to fully level in the Rogue and Barbarian classes simultaneously while everyone else only gets a single class. It's just too many really good things.
Acid Immunity is too good while Acid Breath is too weak. Added onto the previous two abilities, this is gilding the lily.
Frightful Appearance is an interesting and internally balanced ability.
Languages needs to include Common or the race isn't playable except in a joke campaign.
Monster Origin reads like you expected it to be a weakness when it's actually a powerful buff.