Which of the following is the most active metal?

(A) Lithium

(B) Sodium

(C) Potassium

(D) Rubidium

To determine which of the metals listed is the most active, we need to consider the reactivity trends of alkali metals. Alkali metals are found in Group 1 of the periodic table, and their reactivity increases as you move down the group. This is due to the increasing atomic size and the decreasing ionization energy, which makes it easier for these metals to lose their outermost electron.

Understanding Alkali Metal Reactivity

Let's break down the options:

• Lithium (Li) - The lightest alkali metal, it has a relatively low reactivity compared to others in the group.
• Sodium (Na) - More reactive than lithium, sodium reacts vigorously with water and air.
• Potassium (K) - Even more reactive than sodium, potassium reacts explosively with water.
• Rubidium (Rb) - This metal is highly reactive, even more so than potassium, and can ignite spontaneously in air.

Comparative Reactivity

As we move from lithium to rubidium, the reactivity increases. This is because the outer electron is further from the nucleus in heavier alkali metals, making it easier to lose that electron and participate in chemical reactions. For example, potassium reacts with water to produce hydrogen gas and potassium hydroxide, while rubidium does so even more vigorously, often resulting in flames and explosions.

Final Analysis

Considering the trend of increasing reactivity down the group, rubidium is the most active metal among the options provided. Therefore, the answer to your question is:

(D) Rubidium

This understanding of periodic trends not only helps in predicting the behavior of these metals but also illustrates the fascinating nature of chemical reactivity in general.