Which one of the following statements is correct about diamond and graphite?
- A.Diamond and graphite have similar physical and chemical properties.
- B.Diamond is hard but graphite is smooth and slippery.
- C.Diamond and graphite are both non-conductors of electricity.
- D.Both diamond and graphite have similar structures.
Correct answer
Explanation
The correct answer is B, Diamond is hard but graphite is smooth and slippery. Both are pure forms of carbon, but their atoms are arranged differently, which gives them opposite physical properties.
Diamond and graphite are allotropes of carbon. In diamond, each carbon atom is bonded to four others in a rigid three-dimensional network, which makes it the hardest natural substance. In graphite, each carbon atom is bonded to three others to form flat hexagonal layers, and these layers are held together only by weak forces, so they slide over each other. That is why graphite feels slippery and is used as a dry lubricant and in pencil leads.
A is wrong because their physical properties are very different, though chemically both burn to give carbon dioxide. C is wrong because graphite conducts electricity, thanks to the free electron left on each carbon atom; only diamond is a non-conductor. D is wrong because diamond has a tetrahedral network while graphite has layered sheets.
Exam tip: diamond has four bonds per carbon, is hardest and does not conduct; graphite has three bonds, slippery layers and does conduct.
Practice Questions
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- B.Alpha and Gamma radiations only
- C.Beta and Gamma radiations only
- D.Alpha, Beta and Gamma radiations
Show answer
Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.
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- D.Facilitated transport requires assistance of carrier proteins.
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- B.Murray Gell-Mann
- C.Albert Einstein
- D.Niels Bohr
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- A.Kinetochore
- B.Chromonema
- C.Telomere
- D.Centriole
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- A.Hydrogen oxide
- B.Deuterium dioxide
- C.Deuterium oxide
- D.Heavy hydrogen oxide
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