31. In which of the following activities silicon carbide is useD.
A. Making cement and glass
B. Disinfecting water of ponD.
C. cutting very hard substances
D. Making casts for statues
Answer:
C. cutting very hard substances

32. The average salinity of sea water is
A. 3%
B. 3.5%
C. 2.5%
D. 2%
Answer:
B. 3.5%

33. Which of the following was to be discovered first in the chromospheres of the sun?
A. Krypton
B. Xenon
C. Neon
D. Helium
Answer:
D. Helium

34. Which of the following is in liquid form at room temperature?
A. Lithium
B. Sodium
C. Francium
D. Cerium
Answer:
C. Francium

35. The filament of an electric bulb is made of
A. tungsten
B. nichrome
C. graphite
D. iron
Answer:
A. tungsten

36. Diamond is an allotropic form of
A. germanium
B. carbon
C. silicon
D. sulphur
Answer:
B. carbon

37. Bell metal is an alloy of
A. nickel and copper
B. zinc and copper
C. brass and nickel
D. tin and copper
Answer:
D. tin and copper

38. The main constituents of pearls are
A. calcium oxide and ammonium chloriD.
B. calcium carbonate and magnesium carbonate
C. aragonite and conchiolin
D. ammonium sulphate and sodium carbonate
Answer:
B. calcium carbonate and magnesium carbonate

39. Amalgams are
A. highly coloured alloys
B. alloys which contain mercury as one of the contents
C. alloys which have great resistance to abrasion
D. alloys which contain carbon
Answer:
B. alloys which contain mercury as one of the contents

40. Which of the following is the lightest metal?
A. Mercury
B. Lithium
C. Lead
D. Silver
Answer:
B. Lithium

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