The missing reagents are.
Potassium + Iodine = Potassium iodide
Calcium + oxygen = Calcium oxide
Beryllium + Bromine = Beryllium bromide
Copper + Oxygen = Copper oxide
Explanation:
The balanced equation can be written as:
1.Potassium + Iodine = Potassium iodide
![2K(s)+I_{2}(s)\rightarrow 2KI(s)](/tpl/images/0462/9758/b73e5.png)
Here K = potassium
I2 = Iodine
KI = potasssium iodide.
2.Calcium + oxygen = Calcium oxide
![2Ca(s)+O_{2}(g)\rightarrow 2CaO(s)](/tpl/images/0462/9758/1b1a2.png)
Ca = calcium
O2 = oxygen
CaO = Calcium Oxide
3.Beryllium + Bromine = Beryllium bromide
![Be(s)+Br_{2}(g)\rightarrow BeBr_{2}(s)](/tpl/images/0462/9758/351c6.png)
Here,
Be = beryllium
Br2 = bromine
BeBr2 = Beryllium Bromide
4. Copper + Oxygen = Copper oxide
![2Cu(s)+O_{2}(g)\rightarrow 2CuO(s)](/tpl/images/0462/9758/4bdea.png)
Cu = Copper
O2 = oxygen
CuO = Copper Oxide