Why dont ELECTRONS does not exist inside the NUCLEUS of an ATOM?
First off, whoever told you “centripital & centrifugal force” keeps electrons from falling into the nucleus is full of it. Electrons CAN and DO get captured by the nucleus. This process is called inverse beta decay. It doesn’t happen often, but it does happen when the electron cloud is unbalanced to where a lone electron gets sucked into a proton, and that proton becomes a neutron, thus changing the atom into another element. Now to answer you current question, by extension of what is presented above, electrons DO exist inside the nucleus, inside of the neutron. That is why they are neutral. It has been observed that the half-life of free neutrons is about 15 minutes, after which, the neutron spits out an electron and an antineutrino, and becomes a proton. Protons have not yet been found to decay….and people have looked. There is a lot more physics and higher level math behind why “electrons don’t fall into the nucleus” than some lame “centripetal” garbage that someone else gave you.