Choose the incorrectly spelt word.

Correct option is A

The incorrectly spelt word in the given options is (a) Assidous. The correct spelling of the word is "Assiduous," which means showing great care and perseverance.
Meanings of other words are as follows:
Disapproval - a feeling or expression of strong disapproval or opposition.
Devastation - great destruction or damage, especially over a wide area.
Conjoined - joined together, especially in a pair or pairs; having a common origin or cause.