Salam learners! 

Someone was asking about the difference between هل and أ particales we use for making a question of Yes or No.

Grammatically هل and أ both using for making question of yes or no. In sense, we use هل for making sure about something, other hand the particle of أَ is using for making sure about something, and to make an imagination about it too. Therefore, هل we cannot use it in that situation, let’s take these examples to understand more:
First of all in English:
Sometimes we ask like this: Are you OK or OK? (which means are you really fine, or just a word you use for say fine). Here we are using this question in a metaphor way. we aren’t seriously asking as we do in a normal way.” Are you fine? aren’t you?”
So, in Arabic we have two ways to make this question, then which one should be used?
هَلْ أَنْتَ بِخَيْر أَم بِخَيْر؟
أَ أَنْتَ بِخَير أَمْ بِخَيْر؟
If we come back the last definition, we do understand that:
the هل particle using for making sure about something, and the way of asking should be in a normal way. (no metaphor or imagination on it or about it). That means هل cannot be used.
the second one, we can use it in both situations as we said. So, the second is the correct one.
another example:
هل هَذَا مَنْزِل؟
أَ هَذا مَنزل؟
is this a house?
is this a house?

Here, it’s a normal question, no imagination, no metaphor used. So, the both questions are correct.
Hopefully, I explained as well.
Salam,