Number of compounds in which metal has zero oxidation state

To determine the number of compounds in which the metal has a zero oxidation state, we need to analyze each compound individually and identify the oxidation state of the metal in each case.

1. WO3 (Tungsten trioxide)
In this compound, tungsten is in the +6 oxidation state. Therefore, the metal does not have a zero oxidation state.

2. Ni(CO)4 (Nickel tetracarbonyl)
In this compound, nickel is in the zero oxidation state. The oxidation state of carbon in carbon monoxide is -2, so the oxidation state of nickel must be zero to balance the charges. Therefore, this compound has a metal (nickel) with a zero oxidation state.

3. MoO3 (Molybdenum trioxide)
In this compound, molybdenum is in the +6 oxidation state. Therefore, the metal does not have a zero oxidation state.

4. Fe(CO)5 (Iron pentacarbonyl)
In this compound, iron is in the zero oxidation state. Similar to nickel tetracarbonyl, the oxidation state of carbon in carbon monoxide is -2, so the oxidation state of iron must be zero to balance the charges. Therefore, this compound has a metal (iron) with a zero oxidation state.

5. Cr(CO)6 (Chromium hexacarbonyl)
In this compound, chromium is in the zero oxidation state. Again, the oxidation state of carbon in carbon monoxide is -2, so the oxidation state of chromium must be zero to balance the charges. Therefore, this compound has a metal (chromium) with a zero oxidation state.

6. [Pt(NH3)2Cl2] (Diammine dichloridoplatinum(II))
In this compound, platinum is in the +2 oxidation state. Therefore, the metal does not have a zero oxidation state.

7. Co2(CO)8 (Dicobalt octacarbonyl)
In this compound, cobalt is in the zero oxidation state. The oxidation state of carbon in carbon monoxide is -2, so the oxidation state of cobalt must be zero to balance the charges. Therefore, this compound has a metal (cobalt) with a zero oxidation state.

8. Mn2(CO)10 (Dimanganese decacarbonyl)
In this compound, manganese is in the zero oxidation state. Similar to nickel tetracarbonyl and iron pentacarbonyl, the oxidation state of carbon in carbon monoxide is -2, so the oxidation state of manganese must be zero to balance the charges. Therefore, this compound has a metal (manganese) with a zero oxidation state.

Summary:
Out of the given compounds, the following five compounds have a metal with a zero oxidation state:
- Ni(CO)4 (Nickel tetracarbonyl)
- Fe(CO)5 (Iron pentacarbonyl)
- Cr(CO)6 (Chromium hexacarbonyl)
- Co2(CO)8 (Dicobalt octacarbonyl)
- Mn2(CO)10 (Dimanganese decacarbonyl)