Chemistry
The basic chemical building block of natural rubber obtained from trees is

Neoprene
Vinyl Chloride
Acetylene
Isoprene

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Chemistry
Water is not effective in extinguishing a fire caused by petrol because

Water and petrol react chemically
Water and petrol are miscible with each other
The flame is too hot for water to cool it down
Water and petrol are immiscible with each other and petrol which forms the upper layer continues to burn

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