It will take 5.2 years to decay.
The half life of cobalt-60 is 5.2 years. The half life is the time taken for the mass of the substance to decrease by a half.
here, the amount of remaining substance is 50%,
so, 
n. log (0.5) = log (0.5)
n = 1
So it would take 1 half lives to decay this much, which is 1 x 5.2 which is 5.2 years.
what do you mean by radioactive decay ?
The process through which an unstable atomic nucleus loses energy via radiation is known as radioactive decay, also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration. A material that has unstable nuclei is considered as radioactive.
Learn more about decay here:-
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To completely describe an electron in an atom, four quantum numbers are needed: energy (n), angular momentum (ℓ), magnetic moment (mℓ), and spin (ms). The first quantum number describes the electron shell, or energy level, of an atom.
Answer:
A) solute - NaCl, solvent - water
B) solute - O2 and other gases, solvent - N2
C) solute - ethanol, solvent - water
D) solute - tin, solvent - copper
Explanation:
Solute(s) is/are the minor component(s) in a solution, dissolved in the solvent.
Solvent is the component of a solution that is present in the greatest amount. It is the substance in which the solute is dissolved.
If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).