Find out total number of compounds which on heating undergo redox reactions.
`PbCl_(4),Mg(NO_(3))_(2),HgC_(2)O_(4),Ag_(2)CO_(3),Pb(CN)_(4),Al(OH)_(3),Cu(CN)_(2)`

Explanation

To determine the total number of compounds that undergo redox reactions upon heating from the given list, we will analyze each compound one by one. A redox reaction involves the transfer of electrons, resulting in changes in oxidation states of the reactants.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- PbCl₄ (Lead(IV) chloride)
- Mg(NO₃)₂ (Magnesium nitrate)
- HgC₂O₄ (Mercury(II) oxalate)
- Ag₂CO₃ (Silver carbonate)
- Pb(CN)₄ (Lead(IV) cyanide)
- Al(OH)₃ (Aluminum hydroxide)
- Cu(CN)₂ (Copper(I) cyanide)

2. **Analyze Each Compound**:
- **PbCl₄**: On heating, it decomposes to PbCl₂ + Cl₂.
- Oxidation states: Pb goes from +4 to +2 (reduction), Cl goes from -1 to 0 (oxidation).
- **Redox Reaction**: Yes.

- **Mg(NO₃)₂**: On heating, it decomposes to MgO + NO₂ + O₂.
- Oxidation states: Mg stays at +2, N goes from +5 to +4 (reduction), O goes from -2 to 0 (oxidation).
- **Redox Reaction**: Yes.

- **HgC₂O₄**: On heating, it decomposes to Hg + CO₂.
- Oxidation states: Hg goes from +2 to 0 (reduction), C goes from +3 to +4 (oxidation).
- **Redox Reaction**: Yes.

- **Ag₂CO₃**: On heating, it decomposes to Ag + CO₂ + ½ O₂.
- Oxidation states: Ag goes from +1 to 0 (reduction), O goes from -2 to 0 (oxidation).
- **Redox Reaction**: Yes.

- **Pb(CN)₄**: On heating, it decomposes to Pb(CN)₂ + CN₂.
- Oxidation states: Pb goes from +4 to +2 (reduction), CN goes from -1 to 0 (oxidation).
- **Redox Reaction**: Yes.

- **Al(OH)₃**: On heating, it decomposes to Al₂O₃ + H₂O.
- Oxidation states: Al stays at +3, O stays at -2, H stays at +1.
- **Redox Reaction**: No.

- **Cu(CN)₂**: On heating, it decomposes to CuCN + CN₂.
- Oxidation states: Cu goes from +2 to +1 (reduction), CN goes from -1 to 0 (oxidation).
- **Redox Reaction**: Yes.

3. **Count the Redox Reactions**:
- The compounds that undergo redox reactions upon heating are:
1. PbCl₄
2. Mg(NO₃)₂
3. HgC₂O₄
4. Ag₂CO₃
5. Pb(CN)₄
6. Cu(CN)₂

- Total number of compounds that undergo redox reactions = 6.

### Final Answer:
**Total number of compounds which on heating undergo redox reactions: 6**