Chemistry
Conduction band electrons have more mobility than holes because they

Have negative charge
Are lighter
Need less energy to move them
Experience collision less frequently

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

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

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