a. The two products for the reaction are Potassium Hydroxide and hydrogen gas.
2K₍s₎ +2H₂O₍l₎⇒ 2KOH₍aq) +H₂₍g₎
b. The piece of potassium melts and darts on the surface of the water then bursts into a lilac flame. This is because the reaction is highly exothermic- the heat produced makes the potassium melt.
c. Rubidium that has an electron configuration of 2.8.18.18.1 is extremely reactive with water since it has a very large atomic radius. the big atomic radius makes the outer electron loosely attached to the nucleus and thus it is easily lost during the reaction. Reaction under class conditions may cause an explosion.