In ${ }_{88} R a^{226}$ nucleus, there are

138 protons and 88 neutrons 138 neutrons and 88 protons 226 protons and 88 electrons 226 neutrons and 138 electrons

138 neutrons and 88 protons

${ }_z X^A={ }_{88} R a^{226}$ Number of protons = Z = 88 Number of neutrons = A − Z = 226 − 88 = 138