Bond angle is inversely proportional to the repulstion. lone pair so bond pair bond pair repulstion is less than lone pair lone pair. so NH4 is correct because it contains only bond pair bond pair repulstion

The bond angle in a molecule depends on the number of lone pairs and the number of bonded atoms around the central atom. The greater the repulsion between these groups, the larger the bond angle. Let's analyze each option to determine the bond angle in each molecule.

a) NH3:
- NH3 has a central nitrogen atom bonded to three hydrogen atoms.
- Nitrogen has one lone pair of electrons.
- The lone pair of electrons repels the bonded pairs, causing a decrease in the bond angle.
- The bond angle in NH3 is approximately 107 degrees.

b) SCl2:
- SCl2 has a central sulfur atom bonded to two chlorine atoms.
- Sulfur has one lone pair of electrons.
- The lone pair of electrons repels the bonded pairs, causing a decrease in the bond angle.
- The bond angle in SCl2 is approximately 103 degrees.

c) NH4+:
- NH4+ has a central nitrogen atom bonded to four hydrogen atoms.
- Nitrogen has no lone pairs of electrons.
- The four hydrogen atoms are bonded symmetrically around the nitrogen atom, resulting in a tetrahedral arrangement.
- In a tetrahedral arrangement, the bond angle is approximately 109.5 degrees.
- However, since NH4+ has a positive charge, it loses one electron and becomes a cation.
- As a result, the bond angle in NH4+ increases slightly to approximately 109.5 degrees.

d) PCl3:
- PCl3 has a central phosphorus atom bonded to three chlorine atoms.
- Phosphorus has one lone pair of electrons.
- The lone pair of electrons repels the bonded pairs, causing a decrease in the bond angle.
- The bond angle in PCl3 is approximately 107 degrees.

Among the given options, NH4+ has the maximum bond angle of approximately 109.5 degrees.