The candidate was running for office on a strong platform, confidant that his policies would bring about meaningful change in the constituency.

In the following sentence, four words have been highlighted which may be misspelt or inappropriate in their usage. Mark the erroneous word as the answer and if all the words are correct in their spellings and usage, choose ‘All are correct’ as the correct answer.

The correct answer is confidant.

Let's analyze the sentence to identify the error:

"The candidate was running for office on a strong platform, confidant that his policies would bring about meaningful change in the constituency."

1. running: Used correctly as a verb form meaning participating in an election competition.
2. strong: Used correctly as an adjective describing the platform.
3. confidant: This is an error in word usage/spelling. A confidant is a noun referring to a trusted person with whom one shares secrets or private matters. However, in this sentence, an adjective is required to describe the state of the candidate feeling sure or certain. The correct word should be confident.
4. constituency: Used correctly as a noun referring to a body of voters in a specified area who elect a representative to a legislative body.

Therefore, the word confidant is incorrect and should be replaced with confident.