Answer :
The number of protons in Thorium, 90
The number of neutrons in Thorium, 144
The mass defect for the isotope thorium-234 = 1.85864 amu
Solution : Given,
Atomic mass of Thorium-234 = 234.04360 amu
Mass of a proton = 1.00728 amu
Mass of a neutron = 1.00866 amu
First we have to determine the number of protons present in Thorium.
The atomic number of Thorium = 90
As the number of proton is equal to the atomic number. So, the number of proton is, 90
Now we have to determine the number of neutrons in Thorium.
Number of neutrons = Atomic mass - Atomic number
Number of neutrons = 234 - 90 = 144
Now we have to calculate the mass defect for the isotope Thorium-234.
Formula used :

where,
m = mass defect
n = number of protons
x = number of neutrons
= mass of proton
= mass of neutron
Now put all the given values in the above formula, we get the mass defect.


Therefore, the mass defect for the isotope thorium-234 is, 1.85864 amu