The compound in which nickel has the lower oxidation states is :

Options

A. `Ni(CO)_(4)`
B. `(CH_(3)COO)_(2)Ni`
C. `NiO`
D. `NiCl_(2)(PPh_(3))_(2)`

Answer

To find the compound in which nickel has the lower oxidation state, we will analyze the oxidation states of nickel in the given options one by one.

### Step-by-Step Solution:

1. **Option A: Ni(CO)₄ (Nickel Tetracarbonyl)**
- Let the oxidation state of nickel be \( x \).
- Carbon (C) in carbonyl (CO) is neutral, so it has an oxidation state of 0.
- The overall charge of the compound is 0.
- Therefore, we can set up the equation:
\[ x + 4(0) = 0 \implies x = 0 \]
- The oxidation state of nickel in Ni(CO)₄ is **0**.

2. **Option B: (CH₃CO)₂Ni (Nickel Acetate)**
- Let the oxidation state of nickel be \( x \).
- The acetate ion (CH₃COO) has a charge of -1, so for two acetate ions:
\[ 2(-1) + x = 0 \implies -2 + x = 0 \implies x = +2 \]
- The oxidation state of nickel in (CH₃CO)₂Ni is **+2**.

3. **Option C: NiO (Nickel Oxide)**
- Let the oxidation state of nickel be \( x \).
- Oxygen (O) has an oxidation state of -2.
- The overall charge of the compound is 0:
\[ x + (-2) = 0 \implies x - 2 = 0 \implies x = +2 \]
- The oxidation state of nickel in NiO is **+2**.

4. **Option D: NiCl₂(PPh₃)₂ (Nickel(II) Chloride with Triphenylphosphine)**
- Let the oxidation state of nickel be \( x \).
- Chlorine (Cl) has an oxidation state of -1, and triphenylphosphine (PPh₃) is neutral (0).
- The overall charge of the compound is 0:
\[ x + 2(-1) + 0 = 0 \implies x - 2 = 0 \implies x = +2 \]
- The oxidation state of nickel in NiCl₂(PPh₃)₂ is **+2**.

### Conclusion:
After analyzing all four options, we find that:
- Option A: Ni(CO)₄ → Oxidation state of Ni = 0
- Option B: (CH₃CO)₂Ni → Oxidation state of Ni = +2
- Option C: NiO → Oxidation state of Ni = +2
- Option D: NiCl₂(PPh₃)₂ → Oxidation state of Ni = +2

The compound in which nickel has the lower oxidation state is **Option A: Ni(CO)₄**.