Write out the electron configurations for (a) potassium and (b) cobalt. how many unpaired electrons does each possess?

Cobalt has seven electrons in the d sublevel (count how many spaces over it is.) There are 5 orbitals in the d sublevel so the first 5 electrons each take a different orbital (Aufbau Principle.) Each orbital now has one unpaired electron. The last two pair with two of the 5 leaving 3 unpaired electrons.

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na