Concept:The word "essential" means absolutely necessary or extremely important.
Explanation:In the sentence, "Collaboration is essential to the success of the team", the word "essential" shows that collaboration is a basic requirement for the team to succeed.
Option A: "desired" means wanted, but not necessarily required, so it is not nearest in meaning.
Option C: "effective" means producing a good result, but it describes the outcome rather than a necessity.
Option D: "appropriate" means suitable or proper, which is weaker than "essential" and does not express a strong requirement.
Option B: "indispensable" means absolutely necessary or impossible to do without, which matches the meaning of "essential" exactly.
Therefore, the correct choice is B.
Answer:The correct option is B: indispensable.