Radioactive yes, synthetic no. Radium is found in nature in very small trace amounts usually in uranium ore deposits.
Radium is strongly radioactive.
Rutherfordium is radioactive and a solid, liquid, and gas;)
Radium is a solid, radon is a gas. Both are radioactive.
Yes, radium and polonium are radioactive elements.
As radium is radioactive, radium chloride would also be radioactive. Any compounds make with any radioactive material are radioactive, and they cannot be "not" radioactive. Radioactive material doesn't really care if it is "alone" or in compound; it will be radioactive in any case.
Radium, by a big margin. Radium has no isotopes that are not radioactive, but no naturally occurring isotopes of potassium or sodium are radioactive.
Yes. Radium is actually considered an alkaline earth metal. Its colour is nearly pure white, but when exposed to air, it turns black. Radium is also extremely radioactive. A link is provided to the Wikipedia article on radium.
Dust of the radioactive element Radium.
Ordinary phosphorus found in nature is not radioactive. Like all other elements, radioactive synthetic isotopes of phosphorus have been made.
Your question is meaningless. Radium IS a radioactive element, and its power depends on the context. If you mean "is there an element more radioactive than radium" then yes, there are many, e.g. astatine.
Radon and radium are radioactive.
It doesn't. Radium is radioactive. Radium plus a phosphor glows in the dark.