Wizard Spells Confusion

I am playing a Wizard for the first time - so very familiar with this build. I don’t understand why I can’t use a Melf’s Acid Arrow scroll.

Can anyone explain why this scroll is not usable and what I would need to make it work?

Here is my character build Info so far…

Wizard(15), Elf

Strength: 16
Dexterity: 8
Constitution: 14
Intelligence: 16 (19)
Wisdom: 10
Charisma: 10

Lvl 01: Wizard(1): Spell Focus (Evocation), {Keen Sense, Scribe Scroll}
Lvl 02: Wizard(2): 
Lvl 03: Wizard(3): Greater Spell Focus (Evocation)
Lvl 04: Wizard(4): INT+1, (INT=17)
Lvl 05: Wizard(5): Combat Casting
Lvl 06: Wizard(6): Skill Focus (Spellcraft)
Lvl 07: Wizard(7): 
Lvl 08: Wizard(8): INT+1, (INT=18)
Lvl 09: Wizard(9): Spell Focus (Conjuration)
Lvl 10: Wizard(10): Spell Penetration
Lvl 11: Wizard(11): 
Lvl 12: Wizard(12): INT+1, Quicken Spell, (INT=19)
Lvl 13: Wizard(13): 
Lvl 14: Wizard(14): 
Lvl 15: Wizard(15): Greater Spell Focus (Conjuration), Greater Spell Penetration

As a wizard you are made to select a specialization school. If you choose evocation, transmutation or abjuration, you lose access to conjuration which contains acid arrow spell. You can’t learn it then nor use scrolls with that spell.

On the other hand, game never checks the school for feats so despite you cannot cast it (if you took one of those specializations), you can still take spell focus into that school.

Many thanks for the explanation - totally missed that.