Atoms

(a) Electron revolves around the nucleus of an atom. lt is a stable particle. (b) Proton has positive charge and its mass is 1836 times the electronic mass. In free state, the proton is a stable particle. (c) Neutron carries no charge. lts mass is 1839 times the electronic mass In free state the neutron is unstable (its mean life is about ), but it constitutes a stable nucleus along with proton. (d) particle is helium nucleus whose atomic number is and mass number is . Hence, out of the given four options neutron is most unstable.

Answer (d) elliptical