Answer
The answer is below.
Work Step by Step
Isotones are those chemical species which contains same number of neutrons.
The number of protons in thorium is 90. Calculate the number of neutrons as follows:
\[\begin{align}
& \text{Number of neutrons}=\text{Mass number}-\text{Number of protons} \\
& =236-80 \\
& =146
\end{align}\]
The elements having same number of neutrons are \[^{237}\text{Pa}\], \[^{238}\text{U}\], \[^{239}\text{Np}\], and \[^{240}\text{Pu}\].
