Answer the following questions:
Aarthi records the following observations during different reactions:
| Reaction | Number of reactants | Number of products |
| A | 3 | 1 |
| B | 1 | 3 |
| C | 2 | 2 |
| D | 4 | 1 |
1. Which reaction(s) occurs with the evolution of heat mostly?
2. Which reaction cannot be identified as either combination or decomposition from its pattern?
3. Why is decomposition reaction considered as almost opposite of combination?