Answer question numbers (a) - (d) on the basis of your understanding of the following paragraph and related studied concepts.
Green colour of ferrous sulphate crystals changes on heating.Also the smell of characteristic odour of burning sulphur is felt.
`2FeSO_(4)(s)overset("Heat")(to)Fe_(2)O_(3)(s)+SO_(2)(g)+SO_(3)(g)`
In this reaction, you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferrous sulphate crystals `(FeSO_(4).7H_(2)O)` lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide `(Fe_(2)O_(3))`, sulphur dioxide `(SO_(2))` and sulphur trioxide `(SO_(3))`. Ferric oxide is a solid, while `SO_(2)` and `SO_(3)` are gases. Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses -one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition.
`underset("(Limestone)")(CaCO_(3))(s)overset("Heat")(to)underset("(Quick lime)")(CaO(s))+CO_(2)(g)`
What is the difference between decomposition reaction and thermal decomposition ?

Explanation

When the decomposition of a substance takes place on heating only, it is called thermal decomposition.