Heating which of the following salts in a dry test tube may cause a change in their colour ?

Options

A. `ZnCO_(3)` (white)
B. `Co(NO_(3))_(2). 6H_(2)O` (red)
C. `FeSO_(4).6H_(2)O` (green)
D. `MnSO_(4)` (faint pink)

Explanation

To determine which salts may cause a change in color when heated in a dry test tube, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Zinc Carbonate (ZnCO3)**:
- **Initial Color**: White
- **Reaction upon Heating**: ZnCO3 decomposes into ZnO (zinc oxide) and CO2 (carbon dioxide).
- **Final Color**: ZnO is yellow.
- **Conclusion**: Heating ZnCO3 changes its color from white to yellow.

2. **Analyze Calcium Nitrate Tetrahydrate (Ca(NO3)2·4H2O)**:
- **Initial Color**: Typically colorless or white.
- **Reaction upon Heating**: It decomposes to form CaO (calcium oxide), NO2 (nitrogen dioxide), O2 (oxygen), and H2O (water).
- **Final Color**: CaO is black.
- **Conclusion**: Heating Ca(NO3)2·4H2O changes its color to black.

3. **Analyze Iron(II) Sulfate Hexahydrate (FeSO4·6H2O)**:
- **Initial Color**: Green.
- **Reaction upon Heating**: It decomposes to form Fe2O3 (iron(III) oxide), SO3 (sulfur trioxide), and H2O (water).
- **Final Color**: Fe2O3 is brown.
- **Conclusion**: Heating FeSO4·6H2O changes its color from green to brown.

4. **Analyze Manganese(II) Sulfate (MnSO4)**:
- **Initial Color**: Faint pink.
- **Reaction upon Heating**: It decomposes to form Mn3O4 (manganese(II,III) oxide), SO2 (sulfur dioxide), and O2 (oxygen).
- **Final Color**: Mn3O4 is black.
- **Conclusion**: Heating MnSO4 changes its color from faint pink to black.

### Final Summary:
All four salts (ZnCO3, Ca(NO3)2·4H2O, FeSO4·6H2O, and MnSO4) exhibit a change in color upon heating in a dry test tube.