Elements of group- 15 form compounds in +5 oxidation state. However, bismuth forms only one well characterised compound in +5 oxidation state. The compound is

Options

A. `Bi_2 O_5`
B. `BiF_5`
C. `BiCl_5`
D. `Bi_2 S_5`

Explanation

To solve the question regarding the +5 oxidation state of bismuth in group 15, we can follow these steps:

### Step 1: Understand Group 15 Elements
Group 15 elements include nitrogen, phosphorus, arsenic, antimony, and bismuth. They can exhibit multiple oxidation states, primarily +3 and +5.

**Hint:** Remember that the oxidation states of elements in a group can vary, and understanding their electronic configuration helps.

### Step 2: Identify the Oxidation States
As we move down the group, the stability of the +5 oxidation state decreases, while the stability of the +3 oxidation state increases. This trend is attributed to the inert pair effect, where the s-electrons are less available for bonding in heavier elements.

**Hint:** The inert pair effect is crucial in understanding why heavier elements prefer lower oxidation states.

### Step 3: Focus on Bismuth
Bismuth, being the heaviest element in group 15, predominantly forms compounds in the +3 oxidation state. However, it can also form compounds in the +5 oxidation state, but these are rare.

**Hint:** Consider the unique properties of bismuth compared to other group 15 elements.

### Step 4: Identify the +5 Compound of Bismuth
The only well-characterized compound of bismuth in the +5 oxidation state is bismuth pentafluoride (BiF5). This compound exists due to the high electronegativity and small size of fluorine, which stabilizes the +5 state of bismuth.

**Hint:** Look for compounds that are stable due to the presence of highly electronegative elements.

### Final Answer
The well-characterized compound of bismuth in the +5 oxidation state is **bismuth pentafluoride (BiF5)**.