-1 is the charge that results.
It depends on the type of decay that is taking place if its a β+ it will decay into Mn-52 β- decays into Co-59
The number of years required for 1/4 cobalt-60 to remain after decay is calculated as follows
after one half life 1/2 of the original mass isotope remains
after another half life 1/4 mass of original mass remains
therefore if one half life is 5.3 years then the years required
= 2 x 5.3years = 10.6 years
You must perform stoichiometry! always divide by what you already have (this will make since in a moment)
5.2g Carbon | 1 mole/12.01g/mole | 6.02 x 10^23 atoms/1 mole | = atoms in Carbon
above is the basic stoichiometry set up but your calculation should be (5.2g/12.01g) x (6.02 x 10^23) = 2.61 x 10^23 atoms