I know we use the article "an" before a vowel, but this rule wasn't applied to the first sentence. Could anyone please explain why the article "an" wasn't used before the word "individual" in the first sentence and why it was used in the second sentence?
1. As a teacher he tries to give individual attention to his pupils. (Bangla Academy dictionary)
2. In the United States, the National Guard is a military force within an individual state, which can become part of the national army if there is a war or emergency. (Collins dictionary)