Incorrect spelling, explanation: this form is incorrect because p shouldn’t be doubled if there is no accent on that syllable. Accent in developed comes on second, not last syllable, therefore we do not double the consonant in the last syllable when adding a suffix (develop + -ed = developed). Therefore developped is the wrong spelling.

Correct spelling, explanation: developed is the correct form because the syllable with p (the last syllable) isn’t stressed. Here the second syllable is stressed, so despite p being after consonant-vowel in develop (usually consonant-vowel-consonant combination means that the last consonant is doubled when a suffix is added), developed is the correct form, not developped.

Definition of developed:
verb, past simple and participle form of develop, to become more advanced or to advance sth
This country has got a less developed legal system.
The wind power industry will be developed in the future.

Incorrect spelling

Incorrect spelling

Incorrect spelling