Wade's rule is used to predict the structure of boranes, which are compounds of boron and hydrogen.

Explanation:

Borane B5H9 has 5 boron atoms and 9 hydrogen atoms. Based on Wade's rule, we can predict the structure of B5H9 as follows:

1. Assigning the skeletal framework

The first step is to assign the skeletal framework of the borane based on the number of boron atoms. For B5H9, the skeletal framework is a pentagon (five sides) with one hydrogen attached to each boron atom.

2. Counting the number of valence electrons

Next, we count the total number of valence electrons in the borane. Boron has three valence electrons, and hydrogen has one valence electron. Therefore:

5 boron atoms x 3 valence electrons each = 15 valence electrons

9 hydrogen atoms x 1 valence electron each = 9 valence electrons

Total valence electrons = 24

3. Calculating the number of electron pairs

Based on the number of valence electrons, we can calculate the number of electron pairs in the borane using the following formula:

Number of electron pairs = (total valence electrons) / 2

For B5H9, the number of electron pairs is:

Number of electron pairs = 24 / 2 = 12

4. Determining the structure

Finally, we can determine the structure of the borane based on the number of electron pairs. According to Wade's rule, the most stable structure is the one with the minimum number of adjacent three-center-two-electron (3c-2e) bonds.

For B5H9, the most stable structure with 12 electron pairs is a nido structure, which has 3 adjacent 3c-2e bonds. The nido structure of B5H9 is a pyramid with one boron atom at the apex and the other four boron atoms forming a square base. Each boron atom is attached to two hydrogen atoms, except for the apex boron atom, which is attached to one hydrogen atom.

Therefore, the correct answer is option B - nido structure.