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General ScienceMediumAsked in: NDA · NDA-I 2018, GAT

Which one of the following properties is NOT true for graphite ?

  1. A.Hybridisation of each carbon atom is sp³
  2. B.Hybridisation of each carbon atom is sp²
  3. C.Electrons are delocalized over the whole sheet of atoms
  4. D.Each layer is composed of hexagonal rings

Correct answer

A. Hybridisation of each carbon atom is sp³

Explanation

The correct answer is A, Hybridisation of each carbon atom is sp³. In graphite each carbon atom is sp² hybridised, not sp³, so statement A is the one that is not true.

Each carbon in graphite uses three sp² orbitals to bond with three neighbours in the same plane, forming flat sheets of hexagonal rings. The fourth electron of every atom sits in an unhybridised p orbital, and these electrons spread over the whole sheet. The sheets are held to one another only by weak van der Waals forces, so they slide over each other, which makes graphite soft, slippery and useful as a dry lubricant and in pencils. The free electrons let it conduct electricity. sp³ carbon, bonded to four neighbours in a tetrahedron, is found in diamond.

B is wrong as a choice because sp² hybridisation is true of graphite.

C is wrong as a choice because the delocalised electrons are real and explain graphite's conductivity.

D is wrong as a choice because each layer is indeed built of hexagonal rings.

Exam tip: diamond, sp³, hard, non-conductor; graphite, sp², soft layers, conducts electricity.

Practice Questions

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Q1.General ScienceAsked in: UPSC Civil Services · CSE Prelims 2017, GS Paper IMedium

Consider the following pairs : (Commonly used / consumed materials : Unwanted or controversial chemicals likely to be found in them) 1. Lipstick : Lead 2. Soft drinks : Brominated vegetable oils 3. Chinese fast food : Monosodium glutamate Which of the pairs given above is/are correctly matched ?

  1. A.1 only
  2. B.2 and 3 only
  3. C.1 and 3 only
  4. D.1, 2 and 3
Show answer
Correct answer: D. 1, 2 and 3

Each product has been linked to the chemical paired with it. Lead has been found as a trace contaminant in many lipsticks, coming from colour pigments; since lipstick is swallowed in small amounts, regular use raises concern because lead is a toxic heavy metal that harms the nervous system.

Q2.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is not true for anodizing process?

  1. A.It makes aluminium corrosion resistant.
  2. B.Metals like aluminium, titanium and magnesium can be anodized.
  3. C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
  4. D.It is used in aircraft industry.
Show answer
Correct answer: C. Clean aluminium article is the anode and oxygen gas is evolved at the cathode.

In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.

Q3.General ScienceAsked in: CDS · CDS-II 2016, GKMedium

Which one of the following statements is not correct?

  1. A.The response of the ear to sound of increasing intensity is approximately logarithmic.
  2. B.The sensitivity of the human ear does not vary with the frequency of the sound.
  3. C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
  4. D.Longitudinal waves can travel in all media—solids, liquids and gases.
Show answer
Correct answer: B. The sensitivity of the human ear does not vary with the frequency of the sound.

The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.

Q4.General ScienceAsked in: CDS · CDS-I 2017, GKEasy

Kwashiorkor disease in children is caused by

  1. A.sufficient carbohydrates but less fats in diet
  2. B.sufficient carbohydrates and fats but deficient proteins in diet
  3. C.sufficient vitamins but deficient fats in diet
  4. D.sufficient fats but deficient vitamins in diet
Show answer
Correct answer: B. sufficient carbohydrates and fats but deficient proteins in diet

Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.

Q5.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is the correct order of pH for the given substances?

  1. A.Coffee < Lemon juice < Milk of magnesia < Blood
  2. B.Milk of magnesia < Blood < Coffee < Lemon juice
  3. C.Lemon juice < Blood < Coffee < Milk of magnesia
  4. D.Lemon juice < Coffee < Blood < Milk of magnesia
Show answer
Correct answer: D. Lemon juice < Coffee < Blood < Milk of magnesia

Arranged from most acidic to most basic, the four substances fall in exactly this order. Lemon juice, rich in citric acid, has a pH of about 2 to 2.5.