Neither one of them knew the answer to the difficult question.
which word is the indefinite adjective?

Neither

Explanation:

An indefinite adjective is used to describe a noun in a non-specific sense. The most common indefinite adjectives are any, each, few, many, much, most, several, and some. --- (grammar-monster.com)

either online or traditional classroom can work for students. which is better will depend on students and teacher. students may have trouble following a lesson in classroom while they can study at their own pace online. other students may have trouble staying focus on their own in online classes. teachers are more used to classroom teaching but they may also be more worry about their jobs teaching online classes and work harder.

we need to see the document to answer the question