Shouldn't "Er det min?" be accepted?
It is now, although you should probably write "Er det mitt" instead.
why does " er det mitt?" work better than "Er det min" ?
They should be of the same gender, like "er den min" or "er det mitt".
So det is used for neuter objects and den is not?
'det' can also be used as a formal subject, for instance when introducing new things to a conversation: "det er en stol".
Then why is "er det min" right? The current options do not include the two that you mention.
They should, but as you've noticed, 'er det min' is accepted. But this doesn't really follow any of the rules, and is merely an exception, where 'det' is an unspecified object.
It looks like they just got rid of this choice.
Hmm, "er det min" isn't accepted for me.
Thanks, seems I made a typo...
6/2019 - I was confused about how to choose from min/mitt/mi with no context for what "it" was. "er det min" is accepted, although I kicked myself reading fveldig's explanation.
Why isn't it "mitt"?