Chemistry
Atoms of different elements have

Same atomic number and same electronic configuration
Different atomic number and same eletronic configu-ration
Different atomic number and different number of valence electrons
Same number of electrons and neutrons

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Chemistry
Why is water not suitable for putting out a petrol fire ?

Water, being heavy, slips below petrol which thus remains in contact with air and burns
Petrol is too inflammable to be extinguished by water
The oxygen content of water is isolated by petrol and thus it helps in burning
The heat required for combustion of petrol is very low

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