Which one of the following is a metalloid ?
- A.Germanium
- B.Coke
- C.Iodine
- D.Sugar
Correct answer
Explanation
The correct answer is A, Germanium. Germanium is a metalloid, an element whose properties lie between those of metals and non-metals. It is a hard, shiny, grey-white solid like a metal, yet it is brittle and conducts electricity far less well than a metal, which makes it a semiconductor. Germanium, element 32 in group 14, was used in the first transistors, and is still used in fibre optics and infrared lenses. The common metalloids are boron, silicon, germanium, arsenic, antimony and tellurium, lying along the zig-zag line that separates metals from non-metals in the periodic table. Option B is wrong because coke is an impure form of carbon made by heating coal, and carbon is a non-metal. Option C is wrong because iodine, though it has a metallic lustre, is a halogen and a non-metal. Option D is wrong because sugar, or sucrose, is a compound of carbon, hydrogen and oxygen, not an element at all. Exam tip: the six common metalloids are B, Si, Ge, As, Sb and Te; silicon and germanium are the classic semiconductors.
Practice Questions
View allChlorophyll in photosynthetic prokaryotic bacteria is associated with
- A.plastids
- B.membranous vesicles
- C.nucleoids
- D.chromosomes
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Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.
Read the full explanation →Fat in human body is stored in
- A.Adipose tissue
- B.Red blood cells
- C.Muscle tissue
- D.Epithelial tissue
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Adipose tissue is a loose connective tissue whose cells, called adipocytes, are built to store fat. Each cell holds a large droplet of fat that pushes the nucleus and cytoplasm to one side.
Read the full explanation →A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statements is not correct?
- A.The wavelength of X-ray photon is less than the wavelength of visible radiation photon.
- B.Both the photons have different energies.
- C.The speeds of both the photons in vacuum are different.
- D.The frequency of X-ray photon is higher than the frequency of visible radiation photon.
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This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second.
Read the full explanation →Which of the following substances cause temporary hardness in water?
1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
- A.3 and 4
- B.2 and 3
- C.1 and 4
- D.1 and 2
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Temporary hardness is caused by the bicarbonates of magnesium and calcium, Mg(HCO3)2 and Ca(HCO3)2. It is called temporary because simple boiling removes it: on heating, the soluble bicarbonates break down into insoluble carbonate or hydroxide, carbon dioxide and water, and the solid settles out.
Read the full explanation →When a convex lens produces a real image of an object, the minimum distance between the object and image is equal to
- A.the focal length of the convex lens
- B.twice the focal length of the convex lens
- C.four times the focal length of the convex lens
- D.one half of the focal length of the convex lens
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The gap between an object and its real image is smallest when the object is placed at 2F, twice the focal length from the lens.
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