The chart is about atomic structure: at the top, the left box is "nucleus" and the right is "electron cloud".
On the left, under nucleus, the two boxes are: "protons" on the right and "neutrons" on the left. Under proton is elements which is given and under neutrons, it is "isotopes".
On the right, under electron cloud, the next box is "electrons" and then the lower box is "ions".
An atom is made up of a dense nucleus (left) and electron cloud (right) whirling around the nucleus.
Within the nucleus, there are protons (left) and neutrons (middle). Within the electron cloud are the electrons (right most).
If the number of neutrons is different but the no. of protrons is the same, that is called isotope (left). If a neutral atom gains or loses, it becomes an ion (right).
The two elements that produce background radiation on earth are Radon and Uranium. Airborne radon can decay on its own. Radon undergoes alpha decay to produce Polonium. Uranium naturally undergoes alpha decay to produce Thorium.
