Chapter – 18 Pollution of Air and Water Pollution: An undesirable change in the physical, chemical or biological characteristics ...

Chapter – 2 Micro-organisms: Friend and Foe Micro-organisms: Micro-organisms aretoo small andare not visible to the unaided eye. Theycan...

Chapter – 4 Materials: Metals and Non-Metals Metals arestrong and durable. Thus metals areused so widely for making almost everything...