Q11 of 79 Page 3

i) Among iron and aluminium which rusts easily?
ii) What are the conditions, necessary for rusting of iron?

i) Among iron and aluminium, iron rusts easily. It forms Al2O3. That is why iron pipes are wrapped with aluminium metal to prevent rusting of iron.ii) 1) Air or oxygen 2) Water, containing dissolved air.
These are necessary conditions for rusting of iron.

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9 Write the name of the compound, when iron is corroded? 10 Give reasons for the following
i. Na, K and Ca metals form hydrides by combination with hydrogen gas, but most other metals do not.
ii. Aluminium easily combines with oxygen but still it can be used for making kitchen utensils. 12 Name an ore of zinc other than zinc oxide. By what process can this ore be converted to zinc oxide. 13 What property of hydrogen is observed in the following experiments?
i) Balloon, filled with hydrogen, floats.
ii) Pop sound is heard when a burning splint is introduced at the mouth of hydrogen filled jar.
iii) When black cupric oxide is heated in a stream of hydrogen, reddish colour is obtained.