Questions & Answers about Er fragt, ob die Aufgaben gut verteilt sind.
Why does this sentence use sind instead of werden for the passive?
This is the stative passive (Zustandspassiv), the focus of your current lesson. Using a form of sein (here, sind) plus the past participle (verteilt) describes a completed state. He wants to know if the distribution is already finished and looks good. If the sentence used werden (... ob die Aufgaben gut verteilt werden), it would be the process passive, meaning he is asking if the tasks are currently in the process of being distributed.
Why is sind placed at the very end of the sentence?
The word ob (whether/if) introduces a subordinate clause, which always pushes the conjugated verb to the very end. In a normal main clause, the verb is in the second position: Die Aufgaben sind gut verteilt. But because of ob, the conjugated verb sind gets pushed past the participle verteilt to the end of the clause.
Could I use wenn instead of ob here, since they both translate to "if"?
No, you must use ob in this sentence. In German, ob is used for indirect yes/no questions (meaning "whether"). wenn is used for conditions (meaning "in the event that") or time (meaning "whenever"). A good rule of thumb: if you can replace "if" with "whether" in English, always use ob in German.