How many of the following will volatilize on heating leaving no solid residue ?
`(i) NaNO_(3) " " (ii) NH_(4)NO_(3) " " (iii)Ca(H_(2)PO_(2)) " " (iv) NH_(4)HCO_(3)`
(v)`N_(2)H_(5)HSO_(3) " " (vi)AlCl_(3) " " (vii) [Cu(NH_(3))_(4)]SO_(4) " " (viii) FeSO_(4), 7H_(2)O`

Explanation

To determine how many of the given compounds will volatilize on heating leaving no solid residue, we will analyze each compound one by one.

1. **NaNO₃ (Sodium Nitrate)**:
- On heating, NaNO₃ decomposes to form NaNO₂ (sodium nitrite) and O₂ (oxygen gas).
- **Reaction**: 2 NaNO₃ → 2 NaNO₂ (s) + O₂ (g)
- **Conclusion**: Solid residue (NaNO₂) remains.

2. **NH₄NO₃ (Ammonium Nitrate)**:
- On heating, NH₄NO₃ decomposes to form N₂O (nitrous oxide) and O₂ (oxygen gas).
- **Reaction**: 2 NH₄NO₃ → N₂O (g) + O₂ (g)
- **Conclusion**: No solid residue remains.

3. **Ca(H₂PO₂)₂ (Calcium Dihydrogen Phosphate)**:
- On heating, it decomposes to form calcium hydroxide, O₂, and P₄ (phosphorus).
- **Reaction**: Ca(H₂PO₂)₂ → Ca(OH)₂ (s) + O₂ (g) + P₄ (s)
- **Conclusion**: Solid residue (Ca(OH)₂ and P₄) remains.

4. **NH₄HCO₃ (Ammonium Bicarbonate)**:
- On heating, it decomposes to form ammonia gas and CO₂ (carbon dioxide).
- **Reaction**: NH₄HCO₃ → NH₃ (g) + CO₂ (g)
- **Conclusion**: No solid residue remains.

5. **N₂H₅HSO₃ (Hydrazine Sulfite)**:
- On heating, it decomposes to form N₂H₄ (hydrazine), O₂, and SO₂ (sulfur dioxide).
- **Reaction**: N₂H₅HSO₃ → N₂H₄ (g) + O₂ (g) + SO₂ (g)
- **Conclusion**: No solid residue remains.

6. **AlCl₃ (Aluminum Chloride)**:
- On heating, it sublimates to form gaseous AlCl₃.
- **Conclusion**: No solid residue remains.

7. **[Cu(NH₃)₄]SO₄ (Copper(II) Ammonium Sulfate)**:
- On heating, it decomposes to form solid copper sulfate, ammonia, and O₂.
- **Reaction**: [Cu(NH₃)₄]SO₄ → CuSO₄ (s) + NH₃ (g) + O₂ (g)
- **Conclusion**: Solid residue (CuSO₄) remains.

8. **FeSO₄·7H₂O (Iron(II) Sulfate Heptahydrate)**:
- On heating, it loses water and decomposes to form FeSO₄ (solid) and O₂.
- **Reaction**: FeSO₄·7H₂O → FeSO₄ (s) + O₂ (g)
- **Conclusion**: Solid residue (FeSO₄) remains.

Now, let's summarize the results:
- Compounds that leave no solid residue upon heating: NH₄NO₃, NH₄HCO₃, N₂H₅HSO₃, AlCl₃.
- Compounds that leave solid residue: NaNO₃, Ca(H₂PO₂)₂, [Cu(NH₃)₄]SO₄, FeSO₄·7H₂O.

**Final Count**: 4 compounds will volatilize on heating leaving no solid residue.