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Disorders of the Digestive System - Causes, Symptoms & Treatment Disorders of the Digestive System: Causes, Symptoms, Treatment & Prevention 1. Introduction to Digestive Disorders The digestive system breaks down food and absorbs nutrients. Disorders like acid reflux, IBS, or ulcers can interfere with these processes. Understanding symptoms, causes, and treatments is essential for maintaining gut health. 2. Common Digestive System Disorders Acid Reflux (GERD): Stomach acid flows into the esophagus causing heartburn. Peptic Ulcers: Open sores in the stomach or small intestine. Irritable Bowel Syndrome (IBS): Affects bowel habits with cramping and bloating. Constipation: Infrequent or painful bowel movements. Diarrhea: Loose, frequent stools. Inflammatory Bowel Disease (IBD): Includes Crohn's disease and ulcerative colitis. Gallstones: Block bile flow, causing pain an...
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Class 9 Chemistry chapter 3 chemical bonding - Mcqs Answers

 

Exercise 1: Multiple Choice Questions

1. When molten copper and molten zinc are mixed together, they give rise to a new substance called brass. Predict what type of bond is formed between copper and zinc.

  • (a) Coordinate covalent bond
  • (b) Ionic bond
  • (c) Metallic bond ✅
  • (d) Covalent bond

Explanation:

Brass is an alloy, a mixture of two metals (copper and zinc). In metallic bonding, metal atoms release some of their outer electrons, forming a "sea of delocalized electrons" that holds the metal atoms together. This bonding allows metals to conduct electricity, be malleable, and form alloys like brass. Since copper and zinc are both metals, the bonding between them in brass is metallic bonding.

2. Which element is capable of forming all three types of bonds: covalent, coordinate covalent, and ionic?

  • (a) Carbon
  • (b) Oxygen ✅
  • (c) Magnesium
  • (d) Silicon

Explanation:

Oxygen is a very versatile element that can form different types of bonds:

  • Covalent bond: Oxygen forms covalent bonds in molecules like O₂ (oxygen gas) and H₂O (water).
  • Coordinate covalent bond: In H₃O⁺ (hydronium ion), oxygen donates a lone pair of electrons to a hydrogen ion, forming a coordinate covalent bond.
  • Ionic bond: Oxygen can gain two electrons to form O²⁻ ions, which combine with metals like magnesium to form MgO (magnesium oxide), an ionic compound.

3. Why is H₂O a liquid while H₂S is a gas?

  • (a) Because in water, the atomic size of oxygen is smaller than that of sulphur
  • (b) Because water is a polar compound and there exists strong forces of attraction between its molecules ✅
  • (c) Because H₂O molecule is lighter than H₂S
  • (d) Because water can easily freeze into ice

Explanation:

Water (H₂O) is a liquid at room temperature, while hydrogen sulfide (H₂S) is a gas. This is due to the strong hydrogen bonding in water molecules. Hydrogen bonding is an intermolecular force that occurs when hydrogen is bonded to highly electronegative elements like oxygen (O), nitrogen (N), or fluorine (F).

In contrast, H₂S does not form hydrogen bonds because sulfur is less electronegative than oxygen. Instead, it has weaker dipole-dipole interactions, making H₂S molecules easier to separate, so it exists as a gas at room temperature.

4. Which of the following bonds is expected to be the weakest?

  • (a) C – C
  • (b) Cl – Cl
  • (c) O – O ✅
  • (d) F – F

Explanation:

The O-O bond is weaker than the others due to lone pair repulsion. Oxygen atoms have two lone pairs of electrons, which repel each other and weaken the bond.

  • C–C bond is strong due to effective orbital overlap.
  • Cl–Cl bond is weaker than C–C but still stable.
  • F–F bond is weak due to repulsions between fluorine atoms, but the O–O bond is even weaker because oxygen atoms are larger and have more lone pair repulsion.

5. Which form of carbon is used as a lubricant?

  • (a) Coal
  • (b) Diamond
  • (c) Graphite ✅
  • (d) Charcoal

Explanation:

Graphite is used as a lubricant because of its layered structure. Each carbon atom in graphite is bonded to three other carbon atoms, forming hexagonal sheets. These layers are held together by weak Van der Waals forces, allowing them to slide over each other, making graphite an excellent dry lubricant.

6. Keeping in view the intermolecular forces of attraction, indicate which compound has the highest boiling point.

  • (a) H₂O ✅
  • (b) H₂S
  • (c) HF
  • (d) NH₃

Explanation:

Water (H₂O) has the highest boiling point because of strong hydrogen bonding. The strength of hydrogen bonding in water is greater than in HF (hydrofluoric acid) and NH₃ (ammonia) because each water molecule can form four hydrogen bonds, while HF and NH₃ can form only one or two.

H₂S, on the other hand, lacks hydrogen bonding, so its boiling point is much lower.

7. Which metal has the lowest melting point?

  • (a) Li
  • (b) Na
  • (c) K
  • (d) Rb ✅

Explanation:

Rubidium (Rb) has the lowest melting point because as you move down Group 1 (alkali metals), atomic size increases, and metallic bonds become weaker. Weaker bonds require less energy to break, so the melting point decreases.

8. Which ionic compound has the highest melting point?

  • (a) NaCl
  • (b) KCl
  • (c) LiCl ✅
  • (d) RbCl

Explanation:

LiCl has the highest melting point because lithium ions (Li⁺) are small and highly charged, resulting in stronger electrostatic forces between Li⁺ and Cl⁻. Stronger ionic bonds require more heat to break, increasing the melting point.

9. Which compound contains both covalent and ionic bonds?

  • (a) MgCl₃
  • (b) NH₂Cl ✅
  • (c) CaO
  • (d) PCl₃

Explanation:

NH₂Cl (Chloramine) contains both types of bonds:

  • Covalent bonds exist within the NH₂ (amine group) where nitrogen and hydrogen share electrons.
  • Ionic bond is present between NH₂⁺ and Cl⁻, as chlorine gains an electron and forms an ion.

10. Which among the following has a double covalent bond?

  • (a) Ethane (C₂H₆)
  • (b) Methane (CH₄)
  • (c) Ethylene (C₂H₄) ✅
  • (d) Acetylene (C₂H₂)

Explanation:

Ethylene (C₂H₄) has a double covalent bond between the two carbon atoms.

  • Ethane (C₂H₆) has a single bond (C–C).
  • Methane (CH₄) has only single bonds.
  • Acetylene (C₂H₂) has a triple bond (C≡C).

Final Summary:

  • Metallic bonds occur in alloys like brass.
  • Oxygen forms all three types of bonds.
  • Water is a liquid due to hydrogen bonding, while H₂S is a gas.
  • Oxygen-oxygen bonds are weak due to lone pair repulsion.
  • Graphite is a lubricant due to its layered structure.
  • Water has the highest boiling point among H₂O, H₂S, HF, and NH₃.
  • Rubidium has the lowest melting point in alkali metals.
  • LiCl has the highest melting point among NaCl, KCl, LiCl, and RbCl.
  • NH₂Cl has both ionic and covalent bonds.
  • Ethylene (C₂H₄) has a double covalent bond.


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