6. The hardest substance available on earth is :
(a) Gold
(b) Coal
(c) Diamond
(d) Platinum
7. Tetraethyl lead is used as :
(a) pain killer
(b) fire extinguisher
(c) mosquito repellent
(d) petrol additive
8. When an iron nail gets rusted, iron oxide is formed :
(a) without any change in the weight of the nail
(b) with decrease in the weight of the nail
(c) with increase in the weight of the nail
(d) without any change in colour or weight of the nail
9. Among the various allotropes of carbon :
(a) coke is the hardest, graphite is the softest
(b) diamond is the hardest, coke is the softest
(c) diamond is the hardest, graphite is the softest
(d) diamond is the hardest, lamp black is the softest
10. The group of metals Fe, Co, Ni may best called as :
(a) transition metals
(b) main group metals
(c) alkali metals
(d) rare metals
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