## Chemistry and Chemical Reactivity (9th Edition)

$_{27}^{57}Co$, $_{27}^{58}Co$ and $_{27}^{60}Co$ respectively.
From the periodic table for cobalt (Co) $Z=27$ Since $A=Z+n$, with the given number of neutrons of 30,31 and 33, the mass numbers are $A=57$, $A=58$, $A=60$, respectively, so their symbols are: $_{27}^{57}Co$, $_{27}^{58}Co$ and $_{27}^{60}Co$ respectively.