Which one of the following elements is a non-metal but is lustrous ?
- A.Carbon
- B.Silicon
- C.Germanium
- D.Iodine
Correct answer
Explanation
The correct answer is D, Iodine. Iodine is a non-metal, yet its solid crystals have a shiny, metallic lustre, which makes it the standard exception taught in school chemistry.
Non-metals are usually dull, brittle and poor conductors of heat and electricity. Iodine, a halogen in group 17, breaks the rule on lustre: its grey-black crystals shine, and on gentle heating they sublime into a violet vapour. Tincture of iodine is used as an antiseptic, and iodine is added to common salt to prevent goitre. The textbook list of exceptions among non-metals names iodine for lustre, graphite for conducting electricity and diamond for hardness.
A is wrong because carbon is cited as the exception for conduction (graphite) and hardness (diamond), not as the lustrous non-metal. B is wrong because silicon is a metalloid, with properties between metals and non-metals. C is wrong because germanium is also a metalloid, used as a semiconductor.
Exam tip: Non-metal exceptions: iodine is lustrous, graphite conducts electricity, diamond is the hardest natural substance; bromine is the only liquid non-metal.
Practice Questions
View allThe instrument used for detecting the presence of electric current in a circuit is
- A.Refractometer
- B.Galvanometer
- C.Viscometer
- D.Diffractometer
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A galvanometer detects whether a small electric current is flowing in a circuit and shows its direction. A moving-coil galvanometer has a coil placed between the poles of a magnet.
Read the full explanation →Reverberation is a phenomenon associated with a
- A.multiple refraction of sound.
- B.multiple reflection of sound.
- C.single refraction of sound.
- D.single reflection of sound.
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Reverberation is the persistence of sound in a hall after the source has stopped, caused by repeated reflections from the walls, ceiling and floor.
Read the full explanation →Which one of the following is NOT a basic property of electric charge ?
- A.Charges can be added
- B.Charge is conserved
- C.Charge on a body is always an integral multiple of an electron or a proton charge
- D.Charges can be created and destroyed in an isolated system
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This goes against the conservation of charge: the total charge of an isolated system always stays the same. Electric charge has three basic properties.
Read the full explanation →Which of the following organelles have their own DNA and ribosomes?
- A.Endoplasmic reticulum and Golgi bodies
- B.Mitochondria and Chloroplast
- C.Endoplasmic reticulum and cytoskeleton
- D.Cell wall and nucleolus
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These two organelles carry their own circular DNA and their own small (70S) ribosomes, so they can make some of their own proteins.
Read the full explanation →Which one of the following statements is NOT correct ?
- A.All proteins are enzymes
- B.Mostly enzymes are proteins
- C.All fats are energy rich compounds
- D.Glucose is a common carbohydrate
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This statement is false: enzymes are mostly proteins, but most proteins are not enzymes. Proteins do many jobs in the body.
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