A bazooka or other such shoulder fired anti-armour weapons are technically small arms as well (small arms being anything that can be fired by an individual holding it in their hands or mounted against or on the shoulder), though more specifically they would fall under the light weapons part of...
Very much depends on the type and concentration of acid used and how long it was on the skin before being washed off, though i don't know why they would be using such strong acid in a school environment (at least i think this happened while in school)