This solution is "supersaturated".
A supersaturated solution is a solution that contains a higher than than the concentration of solute, slight unsettling influence or seeding causes crystallization of abundance solute.
Supersaturation is a condition of a solution that contains a greater amount of the dissolved material than could be dissolved by the solvent under ordinary conditions.
d.) Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause electrons in the molecules to increase their electronic energy states.
Explanation:
Microwave: transitions in the molecular rotational levels
Infrared: transitions in molecular vibrational levels
UV/Visible: transitions in electronic energy levels.
I don't know terribly much about radioactive decay, but yes, it WILL decay. If it's half life is 25 days, it will be completely consumed in 50 days. By 100 days, it should be long gone. As far as I know, the reason for this is (besides the simple math which is self-explanatory) the Thorium has so many protons/neutrons, it's unstable and thus undergoes radioactive decay as it cannot maintain stable form.
I hope this helps! :)