The `H-H-H` bond angle in `NH_3` is greater than the `H-As-H` bond angle in `AsH_3`.

Explanation

To understand why the H-H-H bond angle in NH3 is greater than the H-As-H bond angle in AsH3, we can break down the explanation step by step.

### Step 1: Identify the Molecules
We are comparing two molecules: ammonia (NH3) and arsine (AsH3).

### Step 2: Understand the Bond Angles
In NH3, the bond angle between the hydrogen atoms (H-H-H) is approximately 107 degrees. In AsH3, the bond angle (H-As-H) is approximately 92 degrees.

### Step 3: Consider the Central Atom
The central atom in NH3 is nitrogen (N), while in AsH3 it is arsenic (As).

### Step 4: Compare Electronegativity
Nitrogen is more electronegative than arsenic. The electronegativity values are approximately 3.0 for nitrogen and 2.2 for arsenic on the Pauling scale.

### Step 5: Analyze the Effect of Electronegativity on Bond Angles
The higher electronegativity of nitrogen means that the bonding electrons in NH3 are drawn closer to the nitrogen atom. This results in greater electron density around the nitrogen, which increases the repulsion between the hydrogen atoms.

### Step 6: Conclude the Bond Angle Comparison
Due to the increased electron repulsion in NH3, the H-H-H bond angle is greater than the H-As-H bond angle in AsH3. Thus, we can conclude that the bond angle in NH3 is greater than that in AsH3 because of the higher electronegativity of nitrogen compared to arsenic.

### Final Conclusion
The H-H-H bond angle in NH3 is greater than the H-As-H bond angle in AsH3 primarily due to the difference in electronegativity between nitrogen and arsenic.

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