What is the opposite form of  ''valuable'', ''worthwwhile'', ''appealing'', ''practical'', ''practical'' and ''harmful''?

1. What is the opposite form of  ''valuable'', ''worthwwhile'', ''appealing'', ''practical'', ''practical'' and ''harmful''?
2, Where are synonyms of the word ''important"
3. What do you need to improve in your talk about a school that you liked?
4. What improvements do you need in your talk about an achievement that you will never forget?