Is 一个西瓜多少 not OK? Is 钱 really obligatory?
Sorry, to be clear, 钱 is obligatory.
钱 is not obligatory because the phrase still makes sense in both English and Chinese without 钱. The English translation would still be how much is one watermelon.
Why's there no 是:
I expected: 一个西瓜是多少
Isn't the same like 你的电话好吗是多少？
How come 一个西瓜是多少 is not okay?
「一個西瓜多少」not accepted, reported