Ans: (d)
18. Among the various allotropes of carbon: [Investigators"s Exam 1990]
    (a) diamond is the hardest, lamp black is the softest
    (b) diamond is the hardest, coke is the softest
    (c) coke is the hardest, graphite is the softest
    (d) diamond is the hardest, graphite is the softest
Ans: (d)
19. Which of the following is the correct sequence of the following elements in increasing order of their relative densities?
         1) Mercury
         2) Gold
         3) Lead
         4) Aluminium
    (a) 3, 2, 1, 4
    (b) 3, 1, 4, 2
    (c) 4, 1, 3, 2
    (d) 4, 3, 1, 2
Ans: (d)
20. Which one of the following is the basis of modern periodic table?
    (a) Atomic mass
    (b) Atomic number
    (c) Atomic size
    (d) Atomic volume
Ans: (b)
21. The purest form of iron is:
    (a) steel
    (b) cast iron
    (c) Pig iron
    (d) wrought iron
Ans: (d)
22. When an iron nail gets rusted, iron oxide is formed: [CBI1990]
    (a) without any change in the weight of the nail
    (b) with increase in the weight of the nail
    (c) with decrease in the weight of the nail
    (d) without any change in colour or weight of the nail
Ans: (b)
23. Liquefied Petroleum Gas consists of mainly: [Asstt Grade 1990]
    (a) methane, ethane and hexane
    (b) ethane, hexane and nonane
    (c) methane, butane and propane
    (d) methane, hexane and nonane
Ans: (c)
24. The metal that is present in photo films is :
    (a) mercury
    (b) platinum
    (c) magnesium
                                                             358