Chemistry
Iodine value is used to estimate

Hydroxyl groups in oil
Carboxylic groups in oil
Alkali content in oil
Unsaturation in oil

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

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
Water and petrol react chemically

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