Theory:

Desirable change:
The changes that are beneficial for us and the environment are called desirable changes.
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Desirable changes
  
These are changes which we desire to take place.
    Example:
  • Preparation of curd
  • Manure from cow dung and dead plants
  • Ripening of fruits
  • Seasonal changes
  • Germination of seeds
  • Baking of cake
  • Cooking food
Undesirable change:
The changes that are harmful to us and the environment are called undesirable changes.
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Undesirable changes
  
These are changes that we do not desire to take place.
    Example:
  • The burning of a factory
  • Rotting of foodstuff
  • Volcanic eruption
  • Flood
  • Earthquake
  • Rusting of iron articles
Note:
  
1. A change may be beneficial at one moment but unfavourable at another.
The burning of fuel (wood, coal) to generate heat is the desired change.
When a house or a factory is burned, it causes an unfavourable change.
 
2. For some, a change may be beneficial, but it may be destructive for others.
Cutting trees may be desirable for those who require wood, but it is undesirable for animals and the environment since it disrupts the natural equilibrium.