CBSE Class 10 Chemistry Chemical Bonding MCQs Set 08

Answer: (a) NH₄Cl

Explanation:
1. In NH₄Cl the ammonium ion NH₄⁺ has covalent (and coordinate) bonds inside it.
2. NH₄⁺ and Cl⁻ are held together by an ionic bond.

Teacher's Note:
1. Look for a polyatomic ion combined with an oppositely charged ion.
2. CH₄ and H₂ are purely covalent and KCl is purely ionic.

Answer: (b) A⁺B⁻

Explanation:
1. A readily loses one electron to form A⁺ and B readily gains one electron to form B⁻.
2. The compound is therefore ionic, A⁺B⁻.

Teacher's Note:
1. A large difference in electronegativity gives an ionic bond.
2. Electropositive atoms form cations and electronegative atoms form anions.

Answer: (c) 4

Explanation:
1. Carbon has atomic number 6, with configuration 2, 4.
2. The outer shell has 4 electrons.

Teacher's Note:
1. Valence electrons are the electrons in the outermost shell.
2. Four valence electrons let carbon form four covalent bonds.

Answer: (d) Br₂

Explanation:
1. NaCl, MgO and KBr are made of a metal and a non-metal and are ionic.
2. Br₂ is formed by sharing a pair of electrons between two bromine atoms.

Teacher's Note:
1. Two identical non-metal atoms can only share electrons.
2. Compounds of metals with non-metals are usually ionic.

Answer: (a) 6

Explanation:
1. Each nitrogen atom has 5 valence electrons and needs 3 more for an octet.
2. They share three pairs, a triple bond, so 6 electrons are shared.

Teacher's Note:
1. Count shared pairs and double the number.
2. N≡N has one sigma and two pi bonds.

Answer: (b) H₂O

Explanation:
1. In H₂O oxygen has 8 electrons but each hydrogen has only 2.
2. In CO₂, CS₂ and CO every atom reaches 8 electrons.

Teacher's Note:
1. Hydrogen follows the duet rule because its first shell holds only 2 electrons.
2. Always check each atom separately.

Answer: (c) ions held together by electrostatic forces

Explanation:
1. An electrovalent bond forms by transfer of electrons, giving oppositely charged ions.
2. The ions are held in a crystal lattice by electrostatic attraction and the compounds have high melting points.

Teacher's Note:
1. Ionic solids have no separate molecules.
2. High melting point is a typical ionic property.

Answer: (d) ionic, covalent and coordinate

Explanation:
1. N–H bonds in NH₄⁺ are covalent, one of them being a coordinate bond (N donates its lone pair to H⁺).
2. NH₄⁺ and Cl⁻ are linked by an ionic bond.

Teacher's Note:
1. All three bond types occur together in NH₄Cl.
2. A coordinate bond is a covalent bond in which one atom supplies both electrons.

Answer: (a) coordinate bond

Explanation:
1. In a normal covalent bond each atom gives one electron.
2. When one atom supplies both electrons the bond is coordinate (dative).

Teacher's Note:
1. The donor has a lone pair and the acceptor has an empty orbital.
2. It is shown by an arrow from donor to acceptor.

Answer: (b) polar covalent

Explanation:
1. Hydrogen and oxygen share electrons, so the bond is covalent.
2. Oxygen is more electronegative, so the shared pair is pulled towards it and the bond is polar.

Teacher's Note:
1. Different atoms sharing electrons give a polar covalent bond.
2. Identical atoms give a non-polar bond.

Answer: (c) three

Explanation:
1. Two atoms can share one, two or three pairs of electrons.
2. A triple bond is the maximum, as in N≡N and C≡C.

Teacher's Note:
1. Single, double and triple bonds are the only ones met at school level.
2. Each shared pair is one covalent bond.

Answer: (d) N₂O

Explanation:
1. CO₂ has 6 + 16 = 22 electrons.
2. N₂O has 14 + 8 = 22 electrons; NO has 15, N₂O₃ has 38 and NO₂ has 23.

Teacher's Note:
1. Isoelectronic species have the same total number of electrons.
2. Add atomic numbers of all atoms to compare.

Answer: (a) Ne

Explanation:
1. Na⁺ has 11 − 1 = 10 electrons.
2. Ne has 10 electrons; NO has 15, N₂ has 14 and Cl⁻ has 18.

Teacher's Note:
1. An ion has electrons equal to atomic number minus its positive charge.
2. Na⁺ has the configuration 2, 8 of neon.

Answer: (b) oxygen

Explanation:
1. O₂ is formed by sharing two pairs of electrons: O=O.
2. H₂ and Cl₂ have single bonds and N₂ has a triple bond.

Teacher's Note:
1. Oxygen needs two more electrons, so it shares two pairs.
2. Hydrogen and chlorine need one electron; nitrogen needs three.

Answer: (c) carbon tetrachloride

Explanation:
1. NaCl, MgCl₂ and AlCl₃ ionise in water to give free ions.
2. CCl₄ is a covalent compound that does not ionise (and does not dissolve in water).

Teacher's Note:
1. Only ionic or ionising compounds conduct in solution.
2. CCl₄ is a non-electrolyte.

Answer: (d) N₂ and CO

Explanation:
1. N₂ has 14 electrons and CO has 6 + 8 = 14.
2. O₂ has 16, CO₂ has 22.

Teacher's Note:
1. Isoelectronic molecules have the same number of electrons.
2. Both N₂ and CO also have a triple bond.

Answer: (a) ammonium iodide

Explanation:
1. NH₄I contains the NH₄⁺ ion with covalent and coordinate bonds, joined to I⁻ by an ionic bond.
2. The other compounds are simple ionic compounds.

Teacher's Note:
1. Look for the ammonium ion.
2. Ammonium chloride works in exactly the same way.

Answer: (b) CCl₄

Explanation:
1. CCl₄ is formed by sharing electrons between carbon and chlorine, a covalent compound.
2. The others contain metal ions and are ionic.

Teacher's Note:
1. Compounds made entirely of non-metals are usually covalent.
2. CCl₄ is a liquid with a low boiling point.

Answer: (c) H₂

Explanation:
1. H₂ is formed by sharing a pair of electrons between two hydrogen atoms.
2. NaCl, MgO and Na₂S are formed by electron transfer.

Teacher's Note:
1. A molecule of one element is always covalent.
2. Use the metal plus non-metal rule for ionic compounds.

Answer: (d) potassium chloride

Explanation:
1. KCl is an ionic compound, a strong electrolyte, and splits fully into K⁺ and Cl⁻.
2. Alcohol and sugar do not ionise; acetic acid ionises only slightly.

Teacher's Note:
1. Strong electrolytes ionise completely.
2. Weak electrolytes such as acetic acid ionise partly.

Answer: (a) Cr(OH)₃

Explanation:
1. Chromium(III) is Cr³⁺ and hydroxide is OH⁻.
2. Cross-over of valencies gives Cr(OH)₃.

Teacher's Note:
1. Write the symbols with their valencies and cross them over.
2. Put brackets around a radical when its subscript is more than one.