Chemistry
The ionisation energy of hydrogen atom in the ground state is x KJ. The energy required for an electron to jump from 2nd orbit to 3rd orbit is

5x/36
x/6
5x
7.2 x

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

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

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