The mass number of aluminium is 26 and the atomic number of aluminium is 13.
The number of neutrons is given by the difference between the mass number and number of protons.
number of neutrons = mass number - number of protons
Number of protons = 13
Mass number of Aluminium = 26
Therefore number of neutrons = 26-13 = 13.
The atomic number of thorium is 90 and the mass number of thorium is 230 as given in the question
atomic number = number of electrons = number of protons
Therefore the number of electrons in thorium 230 = 90
Number of protons in thorium 230 = 90
Number of neutrons = Mass number - number of protons = 230-90 = 140
