Hi ! First it's كيف الحال　not كيف الخال　 خال = uncle , حال = condition "الحمد لله بخير" is the most used in arabic countries you can response also by : أنا بخير　Ana bikhair : I am fine or you can use only بخير to ask others about them , you can response about yourself and in the same ask them by : أنا بخير و أنتَ ؟　Ana bikhair wa anta ? : i am fine and you ? ( you refers to masculine ) أنا بخير و أنتِ ؟　Ana bikhair wa anti ? : i am fine and you ? ( you refers to feminine ) أنا بخير و أنتما ؟　Ana bikhair wa antuma ? : i am fine and you ? ( you two ) أنا بخير و أنتم ؟　Ana bikhair wa antum ? : i am fine and you ? ( you refers to Masculine Plural ) أنا بخير و أنتن ؟　Ana bikhair wa antunna ? : i am fine and you ? ( you refers to Feminine Plural ) Hope it helps :D

non-muslims may say شكرا ، بخير only

انا بخير والحمد لله. وانت؟ - I am fine, thank God. And you? This can be said by Muslims or non-Muslims to Muslims or non-Muslims. And its كيف الحال or كيف الحالك

"الحمد لله بخير" is an appropriate response for everyone, not only for religious.