Which one of the following statements is not correct?
- (a)Most carbon compounds are good conductors of electricity.
- (b)Bonding in organic compounds is covalent.
- (c)Graphite is used as a lubricant.
- (d)Diamond is an allotrope of carbon.
Correct — A, 'Most carbon compounds are good conductors of electricity.' This is the statement that is NOT correct. Carbon bonds covalently, so most carbon (organic) compounds have no free ions or mobile electrons and are therefore poor conductors — they are typically insulators. The other three statements are all true: bonding in organic compounds is covalent, graphite is a well-known solid lubricant, and diamond is an allotrope of carbon. Since the question asks for the incorrect statement, (a) is the answer.
- (b)Bonding in organic compounds is covalent. — This is true — carbon shares electrons to form covalent bonds — so it is a correct statement and cannot be the 'not correct' answer.
- (c)Graphite is used as a lubricant. — This one is true — graphite's layered structure lets the layers slide over one another, so it is used as a dry lubricant, and cannot be the 'not correct' answer.
- (d)Diamond is an allotrope of carbon. — This one is also true — diamond, graphite, graphene and fullerenes are all allotropes of carbon, so the statement holds.
Carbon forms strong covalent bonds. In carbon compounds the electrons are locked into these bonds, leaving no free charge carriers, so most organic compounds do not conduct electricity. Graphite is the notable exception: as an element (not a compound) it has delocalised electrons that make it a good conductor and a useful lubricant.
The trap is that graphite, a form of carbon, does conduct electricity — which can tempt the sweeping claim that 'carbon compounds conduct'. But graphite is elemental carbon, not a carbon compound; covalent carbon compounds are non-conductors, so statement (a) is false.
- Carbon bonds covalently; most carbon compounds lack free ions or mobile electrons and are poor conductors.
- Graphite (elemental carbon) is an exception — delocalised electrons make it a good conductor and a dry lubricant.
- Diamond, graphite, graphene, fullerenes and carbon nanotubes are allotropes of carbon.
- Diamond is the hardest natural material; graphite is soft and slippery — same element, different structures.
- Assuming that because graphite conducts, 'carbon compounds' conduct — graphite is elemental carbon, not a compound.
- Overlooking that the question asks for the statement that is NOT correct.
A 'which statement is not correct' item testing that covalent carbon compounds are poor conductors while elemental graphite is the conducting exception.
No directly related past PYQ was found.
- practice — not a real PYQ
Which allotrope of carbon is a good conductor of electricity?
- (a)graphite
- (b)diamond
- (c)both graphite and diamond
- (d)neither
Answer(a) graphite — its delocalised electrons conduct, unlike diamond.
- practice — not a real PYQ
Most covalent compounds do not conduct electricity because they
- (a)are always solids
- (b)have no free ions or mobile electrons
- (c)dissolve in water
- (d)are metallic
Answer(b) have no free ions or mobile electrons.