Correct spelling


Correct spelling, explanation: the reason for this spelling is the spelling of the core verb, choose, which is spelled with double o. This is why choosing is the correct form. Chosing is a wrong one, which might be mistaken because of a past simple form of choosechose.

Definition of choosing:
1. noun, selecting one from another
Choosing a party theme is always my favourite thing to do when I organise one!
2. verb, (gerund form of verb choose), to pick among others
Can you stop choosing and deciding already? We’ve been standing in this shop for about 20 minutes now!

Incorrect spelling


Incorrect spelling, explanation: this spelling is incorrect because the original verb from choosing is choose, thus it should be spelled with two vowels o. Chosing is spelled only with one o like the past simple form chose. However gerund/present participle forms are created with -ing added to the core verb, therefore choosing is the only correct form here.