Answer:
Radiation therapy is the use of high energy radiation to kill cancer cells.
A. isotopes only hve different mass which is caused by additional/lesser neutron. protons and electrons number are fixed
Gas are well separated with no regular arrangement. liquid are close together with no regular arrangement. solid are tightly packed, usually in a regular pattern.
Atoms in the same group (column) of the periodic table have similar properties. This is because all elements in the same group have the same amount of valence (outer) electrons.
So, any element directly above or below Calcium on the periodic table would have similar properties.
These would be Magnesium, Barium, Strontium, Radium, and Beryllium.