Day 1: Favourite Series for Arthur 
Season 1 and Season 4

Day 2: Favourite Episode for Arthur
S1E4, S1E11, S2E8, S3E8, S3E12, S3E13, S4E1, S4E2, S4E3, S4E10
I know that's too many...so, S1E11?

Day 3: Favourite Scene for Arthur
S4E3, kissed his father's forehead, opened the door, and told Merlin it was a new day, with sunlight pouring in from the windows behind him

Day 4: Favourite Arthur Quote
S1E11:  You know me, Merlin, I never listen.
S4E01:  I am scared, Merlin, maybe more than you.
Hard to choose

Day 5: Favourite Platonic Relationship
Merlin/Arthur friendship

Day 6: Who You Ship Arthur With Romatically
Merlin...

Day 7: Favourite Tunic of Arthur’s
The red one or the blue one he usually wears in his chamber

Day 8: Favourite Daddy Issue Moment
S4E3: I'm not ready.

Day 9: Favourite Arthur Kiss
S4E3:  he kissed his father on the forehead.
S4E6:  he kissed Merlin on his muddy neck (if that really is a kiss.)

Day 10: Your Favourite of Arthur’s Enemies
Morgana and Mordred

Day 11: Favourite Arthur Fight Scene
S1E2: with Valiant

Day 12: A Scene with Arthur That Made You Laugh
A lot, for example simpleton!Arthur
Or: "They are like giant ... baby rats."  on their way to rescue Gwen

Day 13: A Scene with Arthur That Made You Cry
Actually, none.
But I nearly cried for Merlin in S2E8.

Day 14: A Scene with Arthur You Never Expected
S4E4: the falling of his trousers

Day 15: A Scene with Arthur That Made You Angry
I don't like him treating Merlin like trash, so perhaps something in S2E1.

Day 16: Favourite Knight/Arthur Interaction/Relationship
S1E5: challenging Lancelot with a broomstick
S3E8: Don't be such a princess.
Yes I have a princess kink.><

Day 17: Something You Wish Had Happened for/to Arthur
Maternal affection.

Day 18: Something You Wish Hadn’t Happened for/to Arthur
Betrayal

Day 19: Best Arthur Rage
S2E8: If you choose not to defend yourself, I'll strike you down where you stand.
The sword fight between father and son is really amazing.

Day 20: Favourite Spell Cast On Arthur
Healing spell in S3E12 when he was running a fever.

Day 21: Favourite Quote About Arthur’s Destiny
A half cannot really hate what makes it whole.

Day 22: Favourite Quote About Arthur in General
S1E11: He has proved he is pure of heart.

Day 23: Favourite Bedroom Scene
Throwing a pillow at Merlin but said pillow fell at the feet of Uther.

Day 24: Arthur is Hottest in Series 1/2/3/4
S1 and S4
In S1 that's innocence and boyish vigor, while in S4 it's more mature, and don't forget the TEARS!

Day 25: What You Love Most About Arthur Physically
Fair hair and blue eyes.  They make me want to recite Sonnet 18. orz

Day 26: What You Love Most About Arthur Characteristically
Courage and pure of heart, kindness and tenderness under the tough shell
  
Day 27: Favourite Deleted Scene with Arthur
I don't really know a lot about deleted scenes.  Maybe in S3E13 when he led Merlin to the seat on his right hand at the Round Table.

Day 28: Favourite ‘Arthur You Are Clearly Homosexual’ Scene
Every time he looks at Merlin.  It's all written in the eyes.wwww

Day 29: An Arthur Clearly Needs A Fucking Hug Moment
S4E3: I lost both my parents because of magic.

Day 30: Why Will Arthur Be Albion’s Greatest King IYO?
Because he believes in right not might, and also he is courageous and pure of heart.