Which shows the greatest metallic character?

-Na
-K
-Rb
-Cs

Also,
What ions are very important for the proper functioning of biologic systems such as nerves and muscles?

--oxygen ions
--nitride ions
--alkali metal ions
--alkaline earth metal ions
--hydrogen ions

To determine which element shows the greatest metallic character among Na, K, Rb, and Cs, we need to consider the general trends in metallic character across the periodic table. Metallic character generally increases as you move down a group and decreases as you move across a period from left to right.

In this case, Na is in the second period of the periodic table, K is in the third period, Rb is in the fourth period, and Cs is in the fifth period. Since we are going down a group, the metallic character is expected to increase.

Therefore, Cs (Cesium) exhibits the greatest metallic character among the given elements because it is located furthest down the periodic table.

Moving on to the second question, the ions that are crucial for the proper functioning of biological systems, such as nerves and muscles, are:

- Alkali metal ions: Alkali metals, such as sodium (Na), potassium (K), lithium (Li), and others, play essential roles in maintaining nerve impulses and muscle contractions.

- Alkaline earth metal ions: Alkaline earth metals, such as calcium (Ca), magnesium (Mg), and others, are also important for proper muscle and nerve function.

- Hydrogen ions: Hydrogen ions (H+) are involved in various cellular processes and play important roles in pH balance and the functioning of enzymes.

On the other hand, oxygen ions and nitride ions are not specifically important for the proper functioning of biologic systems such as nerves and muscles.