Acid Splash 3.5e FAQ
Does Acid Splash use touch AC in D&D 3.5e?
Yes. Acid Splash requires a ranged touch attack in D&D 3.5e, so the caster rolls against the target's touch Armor Class rather than its normal Armor Class. Armor, shield, and natural armor bonuses do not apply to touch AC, while modifiers such as Dexterity, size, deflection, dodge, cover, and other applicable defenses can still matter. Acid Splash is therefore often easier to land against heavily armored creatures, but it is never an automatic hit.
Acid Splash is a spell, but it still uses an attack roll to determine whether its acid missile connects. The important difference from an ordinary weapon attack is that Acid Splash is a ranged touch attack, so the relevant defense is touch Armor Class rather than the target's full Armor Class. This distinction matters most against creatures whose protection comes from armor, shields, or natural armor. Those defenses can make a creature difficult to hit with ordinary attacks while doing much less against an effect that only needs to make contact. Touch AC still includes other applicable defenses, however, so the spell should not be treated as though it simply ignores Armor Class altogether.
Acid Splash is a ranged touch attack
Casting Acid 
D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash creates one missile of Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/, but that missile does not automatically strike its target. The caster makes a ranged touch attack, using the normal attack-roll process while comparing the result to the target's armor class 
D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ instead of its normal AC.
If the ranged touch attack fails to hit, Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash deals no damage. If it hits, the spell deals its normal 1d3 
D&D Portal - Dice Roller Roll your dice Roll standard or custom dice with adjustable count, faces, advantage, and disadvantage. Full link: https://dnd-portal.com/dice-roller/ Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/. There is no separate saving throw 
D&D Portal - Saving Throw D20 test rule Saving Throw is a d20 test rule used to resolve
uncertain outcomes during play. Full link: https://dnd-portal.com/rules/d20-tests/saving-throw/ that replaces the attack roll or gives the target another chance to avoid the hit.
The word “touch” can be misleading because the caster does not need to stand next to the target. Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash uses a ranged touch attack, meaning the spell reaches the target at range while still using the touch-attack rules for armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/.
What touch AC ignores
A touch attack represents an attack that only needs to make contact rather than penetrate the target's physical protection. Because of that, armor bonuses, shield bonuses, and natural armor bonuses are not included in the target's touch armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/.
This is why a creature in heavy armor can have an excellent normal armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ but a much lower armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/. The armor still protects the creature from ordinary attacks, but it does not help against an effect that only needs to touch the target.
Natural armor is treated the same way for this purpose. A creature with a thick hide, scales, or another large natural armor bonus may be hard to wound normally while remaining much easier to hit with Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash if its other touch-AC modifiers are modest.
What still applies to touch AC
armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ is not automatically 10. Modifiers that represent avoiding contact or magically deflecting an attack can still contribute, including Dexterity, size, deflection, dodge, and other bonuses or penalties that specifically apply to touch attacks.
A lightly armored but extremely agile creature may therefore have a armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ close to its normal AC. Likewise, a small creature can gain a useful size bonus, and magical effects that provide deflection can remain effective even though armor and shield bonuses do not.
Penalties still matter as well. If a target loses Dexterity to AC or suffers another condition that lowers the modifiers contributing to armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/, Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash may become easier to land even though the spell itself has not changed.
Why touch AC matters for Acid Splash
The use of armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ is one of the main practical advantages of Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash. A heavily armored opponent may be very difficult to hit with a weapon but comparatively easy to touch with a spell attack, allowing Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash to remain relevant even though its damage is only 1d3 D&D Portal - Dice Roller Roll your dice Roll standard or custom dice with adjustable count, faces, advantage, and disadvantage. Full link: https://dnd-portal.com/dice-roller/.
For example, a creature with normal AC 21 and armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ 11 presents two very different targets. An ordinary attack may need to reach AC 21, while Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash only needs to reach 11. The spell gains no extra damage from this difference, but the chance to connect can be substantially better.
That advantage depends entirely on how the target builds its armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/. A creature with normal AC 18 and armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ 17 gains most of its defense from modifiers that still apply to touch attacks, so Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash receives very little practical benefit from targeting armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ in that matchup.
Cover, concealment, and other defenses still matter
Using armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ does not cause Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash to ignore the rest of the ranged-combat rules. Cover can still improve a target’s defense, and concealment can still create a miss chance even when the attack roll would otherwise be high enough to hit armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/.
Line of effect and range also remain relevant. The caster still needs a legal path for the spell and must keep the target within Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash’s Close range. armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ only answers which armor class D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ modifiers apply when the attack roll is resolved.
This is an important distinction when adjudicating the spell: “ranged touch attack” does not mean “ignore defenses.” It means that the attack uses the touch-attack rules while every other applicable combat rule continues to function normally.
Can Acid Splash score a critical hit?
Yes. D&D 3.5e allows damaging spells that require attack rolls to score critical hits, and Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash qualifies because it uses a ranged touch attack and deals hit point damage.
Under the normal critical-hit rules, an attack generally threatens on a natural 20 and uses a ×2 multiplier unless another rule changes those values. For Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash, the spell’s normal 1d3 D&D Portal - Dice Roller Roll your dice Roll standard or custom dice with adjustable count, faces, advantage, and disadvantage. Full link: https://dnd-portal.com/dice-roller/ damage is therefore rolled more than once when a critical hit is confirmed.
The reason is the attack roll, not the fact that the effect is magical. A damaging spell that does not require an attack roll cannot score a critical hit merely because it reduces hit points.