`BrF_3` is a liquid which considerably undergoes self ionization to form cationic and anionic species.Based on VSEPR theory, number of 90 degree F-Br-F bond angles is ……. In anionic species.
`2BrF_3 hArr [BrF_2]^+ + [BrF_4]^(-)`

Explanation

To solve the problem regarding the number of 90-degree F-Br-F bond angles in the anionic species \( \text{BrF}_4^- \), we can follow these steps:

### Step 1: Understand the self-ionization of \( \text{BrF}_3 \)
The self-ionization of \( \text{BrF}_3 \) can be represented as:
\[ 2 \text{BrF}_3 \rightleftharpoons [\text{BrF}_2]^+ + [\text{BrF}_4]^- \]
This indicates that \( \text{BrF}_3 \) can lose a fluorine atom to form a cationic species \( \text{BrF}_2^+ \) and an anionic species \( \text{BrF}_4^- \).

### Step 2: Determine the electron configuration of bromine in \( \text{BrF}_4^- \)
Bromine (Br) has 7 valence electrons. In \( \text{BrF}_4^- \):
- 4 electrons are used to form bonds with 4 fluorine atoms.
- The remaining 3 electrons will include 2 lone pairs and 1 additional electron due to the negative charge.

### Step 3: Identify the molecular geometry using VSEPR theory
According to VSEPR theory, the arrangement of electron pairs around the central atom (Br) determines the molecular geometry.
- We have 4 bond pairs (from the 4 Br-F bonds) and 2 lone pairs.
- The total number of electron pairs is 6 (4 bond pairs + 2 lone pairs).

### Step 4: Determine the hybridization and shape
The hybridization for 6 electron pairs is \( \text{sp}^3\text{d}^2 \), which corresponds to an octahedral arrangement. However, with 2 lone pairs, the molecular shape becomes square planar.

### Step 5: Calculate the bond angles
In a square planar geometry:
- The bond angles between the fluorine atoms around the bromine atom are 90 degrees.

### Step 6: Count the number of 90-degree angles
In \( \text{BrF}_4^- \):
- There are 4 F-Br-F bond angles, and all of them are 90 degrees.

### Final Answer
Thus, the number of 90-degree F-Br-F bond angles in the anionic species \( \text{BrF}_4^- \) is **4**.

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