Transcription: At the level of nucleons, a neutron transforms into a proton with the emission of an electron and an electron anti-neutrino. At this level too, you can see that charge is conserved. Now, can you remember what the quark content of a proton and a neutron are? If you can't, use the particle database to find out. Can you then work out what has changed at the quark level? To check your answer, look at the quark picture for this decay.
(.mp3)