NH4 +.. all r sp³ so same % s character.. but NH4+ has zero lone pair.. so maxm bond angle..

**Answer:**

The bond angle is the angle formed between two adjacent bonds in a molecule. The bond angle is influenced by various factors, including the number of bonding and non-bonding electron pairs around the central atom. Let's analyze the bond angles of the given molecules:

**a. NH3 (Ammonia):**
- Ammonia (NH3) has a trigonal pyramidal molecular geometry.
- The central nitrogen atom has three bonding pairs and one lone pair of electrons.
- The three bonding pairs repel each other and try to maximize the distance between them.
- The repulsion between the bonding pairs and the lone pair causes a decrease in the bond angle.
- The bond angle in NH3 is approximately 107 degrees, which is less than the ideal tetrahedral angle of 109.5 degrees.

**b. NH4+ (Ammonium):**
- Ammonium (NH4+) has a tetrahedral molecular geometry.
- The central nitrogen atom has four bonding pairs and no lone pairs of electrons.
- The four bonding pairs repel each other and try to maximize the distance between them.
- The bond angle in NH4+ is approximately 109.5 degrees, which is the ideal tetrahedral angle.

**c. PCl3 (Phosphorus Trichloride):**
- Phosphorus trichloride (PCl3) has a trigonal pyramidal molecular geometry.
- The central phosphorus atom has three bonding pairs and one lone pair of electrons.
- The three bonding pairs repel each other and try to maximize the distance between them.
- The repulsion between the bonding pairs and the lone pair causes a decrease in the bond angle.
- The bond angle in PCl3 is approximately 107 degrees, which is less than the ideal tetrahedral angle of 109.5 degrees.

**d. SCl2 (Sulfur Dichloride):**
- Sulfur dichloride (SCl2) has a bent molecular geometry.
- The central sulfur atom has two bonding pairs and two lone pairs of electrons.
- The two bonding pairs repel each other and try to maximize the distance between them.
- The repulsion between the bonding pairs and the lone pairs causes a decrease in the bond angle.
- The bond angle in SCl2 is approximately 103 degrees, which is less than the ideal tetrahedral angle of 109.5 degrees.

Based on the above analysis, we can conclude that the bond angle is maximum in **NH4+ (Ammonium)**, where it is approximately 109.5 degrees. This is because it has a tetrahedral molecular geometry with four bonding pairs around the central nitrogen atom.