On motzaei shabbat, I heard the megillah being read from kol chai radio station. I wanted to know if that leining could be considered a true leining? Would I have been yotze from that reading? Why or why not? And if not, why do they lein it from the radio then?

Shalom, Thank you for your question. Much has been written about hearing the migillah via the radio, or even via a loudspeaker (see for example Shut Yechavay Da'at 3,54, and the Tzit Eliezer 4,26). The overwhelming ruling of rabbis today is that one should not fulfill their mitzvah of listening to the migillah via the radio, (though they debate the possibility that perhaps after the fact, or in times of great need, whether one can rely on hearing the megillah via the radio). The main issue at hand is whether what one hears from the radio's speaker is in fact the voice of the person reading. In order to fulfill the mitzvah one needs to hear the reading from someone who is themselves obligated in the mitzvah. So if, for example, one heard the reading from a trained parrot, everyone agrees that the mitzvah was not fulfilled (though that would be some Purim act!). Also, if one heard a recording of the migillah reading, it would not suffice. So, is the electrical reproduction of the broadcast voice from the radio considered as a "voice" of the reader or not? That is the question the rabbis debate when it comes to listening to the migillah via a speaker or radio. Even though we wrote that the main stream ruling is to be strict, it is still a great thing that the national radio station broadcasts the megillah reading (for not only the private religious station broadcast it, but also the national station – Kol Yisrael). This is for two reasons. Firstly, there are opinions that hold that one can fulfill the mitzvah in this way, and it is certainly better than not hearing the megillah at all. So for those people who will not get to a synagogue reading, this is the next best thing. Secondly, even if no one fulfills their mitzvah by the radio reading, it is still a great Kiddush Hashem (sanctification of G-d's name) to have the national radio station's prime time used to broadcast words from the Tanach – may we merit to increase all types of Torah in Israel! Blessings.