Correct spelling, explanation: occasion is the correct form because it originates in Latin occasionem, which is also spelled with double c and one s. Due to the Latin origin, there is no -tion ending, so ocation is incorrect; it’s also lacking double c. Therefore occasion is the correct spelling.

Definition of occasion:
noun, certain time or event; special event
That’s a wonderful occasion to celebrate our anniversary and Jack’s graduation.
On the occasion of her promotion, she treated herself with new shoes.

Phrases with occasion:
on a number of occasions
Yes, we’ve met on a number of occasions.
have occasion to do sth
I’ve never had any occasion to visit Paris.
a sense of occasion
Look at her shorts, she doesn’t have any sense of occasion!

Incorrect spelling, explanation: ocation is a wrong form because we don’t use -tion noun ending here; the word occasion is originally Latin (occasionem), and the double c and one s spelling remained in the English version. Thus occasion is the only possibility here.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling