Final answer:
The reaction of rubidium with water is more vigorous than that of sodium, and the rate of reaction of magnesium is slower than rubidium and sodium.
Step-by-step explanation:
The reaction of rubidium with water is more vigorous than that of sodium. Rubidium and cesium react explosively with water, while sodium reacts more rapidly but may not reach the level of explosion. Therefore, the correct answer is a) More vigorous.
When comparing the rate of reaction of magnesium to rubidium and sodium with water, the reaction of magnesium is slower.
Magnesium reacts at a moderate rate, while rubidium and sodium react more rapidly and may even explode. Therefore, the correct answer is b) Slower.