Dear aspirant

You haven't mentioned any exam name for which you are enquiring, as your profile suggest you are medicine aspirant i assume that your query is related to neet.

Everyone can attend all india quota counseling for that you don't need any domicile certificate, although if you are obtaining seat in category other than Gen, you will need to produce caste certificate.

Now for getting govt medical College in state counseling you need to produce domicile certificate of that particular state from which you belong.

You can participate in Kerala State counseling as non-domicile, you will be eligible only for taking admission private medical colleges there.

Yes you can simultaneously apply in your state quota and also in all india quota counseling, you will be allowed to attend all these three counseling.

Although every counseling have some security deposit which you have to pay, so if you get college you might loose those security money.

Otherwise you can attend all thre counseling,there is no harm in that.

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Hope this information helps you

All the best