Answer:
The missing reagents are.
Potassium + Iodine =<u> Potassium iodide</u>
<u>Calcium</u> + oxygen = Calcium oxide
Beryllium +<u> Bromine</u> = Beryllium bromide
<u>Copper + Oxygen</u> = Copper oxide
Explanation:
The balanced equation can be written as:
1.Potassium + Iodine =<u> Potassium iodide</u>

Here K = potassium
I2 = Iodine
KI = potasssium iodide.
2.<u>Calcium</u> + oxygen = Calcium oxide

Ca = calcium
O2 = oxygen
CaO = Calcium Oxide
3.Beryllium +<u> Bromine</u> = Beryllium bromide

Here,
Be = beryllium
Br2 = bromine
BeBr2 = Beryllium Bromide
4. Copper + Oxygen = Copper oxide

Cu = Copper
O2 = oxygen
CuO = Copper Oxide