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D: NH₄Cl (Ammonium chloride). The bond formed between the nitrogen atom in ammonia and the chloride ion is a coordi nate bond.

(D) nitrogen

4°C is maximum density.

CI < S < N < O < F.

Inter molecular and Intra molecular hydrogen bond.

Orbitals can overlap to a greater extent in a σ-bond due to their axial orientation, so σ-bond is quite strong. On the other hand in a π-bond sideways overlapping is not to an appreciable extent due to the already present σ-bond which restricts the distance between the involved atoms. Hence σ-bonds is much stronger than a π-bond.

It is because extent of overlapping is more in σ-bond than π-bond.

He₂ does not exist because repulsive forces dominate attractive forces and bond order is 0 for He₂.

Correct option is  A) Ionic

The increasing order of energies of molecular orbitals for molecules (except O₂ and F₂) is :

σ1s < σ*1s < σ2s < σ*2s < (π2p_x = π2p_y) < σ2p_z < (π*2p_x = π*2p_y) < σ*2p_z

The increasing order of energy of molecular orbitals for diatomic molecules like O₂ and F₂ is :

σ1s < σ*1s < σ2s < σ*2s < σ2p_z < (π2p_x = π2p_y) < (π*2p = π*2p_y) < σ*2p_z

Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule.

Bond strength represents the extent of bonding between two atoms forming a molecule. The larger the bond energy, the stronger is the bond and the greater is the bond order.

The amount of energy required to break one mole of bonds of a particular type so as to separate them into gaseous atoms is called bond energy.

Bond energy is directly proportional to the bond order. Thus, more the value of bond order, greater will be the bond energy and vice-versa.

1. A neutral atom has bigger in size than its cation.

2. A cation has more protons and nucleus of the cation attracts the electrons in the outermost orbital more. 

3. Hence, the radius of the anion decreases. It means size of the anion decreases. 

4. So, a neutral atom is bigger than its cation.

Ionic bond is a type of chemical bond which involves the transfer of one or more electrons from one ion to another ions of opposite charges.The ion which gains an electron is called as anions, whereas the ion which has loose an electron is called as cation.Mostly the cations are metals & anions are non metal. For eg

Na + Cl → Na⁺ + Cl⁻ → NaCl

(i) Low ionization enthalpy of element forming cation.

(ii) More negative electron gain enthalpy of element forming anion.

(iii) High lattice enthalpy of the ionic compound formed.

When electricity is passed through sodium chloride solution in which carbon rod is immersed hydrogen and chlorine gas are produced. It is an ionic compound. In the second when electricity is passed through sugar solution there is no charge. 

Hence it belongs to covalent compound.

Hydrogen chloride is a gas at room temperature and in dry state it is a bad conductor of electricity.

Bond length :

• Bond length is defined as the equilibrium distance between the nuclei of two covalently bonded atoms in a molecule.
• Each atom of the bonded pair contributes to the bond length.
• Bond length depends upon the size of atoms and multiplicity of bonds. It increases with increase in size of atom and decreases with increase in multiplicity of bond. 
• e.g. C – C single bond is longer than C ≡ C triple bond.
• Bond lengths are measured by X-ray and electron diffraction techniques.

Molecules are not present in ionic substances. Only ions are present. The formula of an ionic substance represents the simpler ratio of ions in one mole of crystal. Hence a more appropriate term is ‘formula weight’.

Hydrogen chloride is a gas. In dry state, it is bad conductor of electricity. Hence, it is a covalent compound.

It is the average angle between two adjacent atoms bonded to the central atom in a molecule. Molecules with larger bond angles are more stable than those with smaller angles.

(b) O₂^2-

O₂^2- is diamagnetic. Additional two electrons are paired in anti-bonding molecular orbits π*_2py and π*_2pz

Hydrogen chloride and hydrogen bromide.

Sulphur dioxide (SO₂) is a diamagnetic molecule because it has all electrons paired (no free electrons).

An ion is an electrically charged atom (or group of atoms).

(i) Y will form an anion

(ii) Z forms a cation

(iii) X has four electrons in its valence shell.

The number of ions of opposite charge that surround a given ion of given charge is known as coordination number of that given ion.

Factors affecting formation of anion or cation are : 

1. Atomic size, 

2. Ionization potential, 

3. Electron affinity, 

4. Electronegativity.

The electronic configuration of X is 1s² 2s² 2p⁶ 3s²3p⁶4s²  

So its valency is 2.

The electronic configuration of Y is  1s² 2s² 2p⁶ 3s² 3p⁵

So its valency is 1. 

∴ The formula of the compound is XY₂

The electronegativity difference of elements = 3 – 1 = 2. So the electronegativity difference is more than 1.9. Therefore the bond formed between the elements is ionic in nature.

Characteristic features of hybrid orbitals :

• Number of hybrid orbitals formed is exactly the same as the participating atomic orbitals.
• They have same energy and shape.
• Hybrid orbitals are oriented in space in such a way that there is minimum repulsion and thus are directional in nature.
• The hybrid orbitals are different in shape from the participating atomic orbitals, but they bear the characteristics of the atomic orbitals from which they are derived.
• Each hybrid orbitals can hold two electrons with opposite spins.
• A hybrid orbital has two lobes on the two sides of the nucleus. One lobe is large and the other small.
• Covalent bonds formed by hybrid orbitals are stronger than those formed by pure orbitals, because the hybrid orbital has electron density concentrated on the side with a larger lobe and the other is small allowing greater overlap of the orbitals.

Conditions for hybridization :

• Orbitals belonging to the same atom can participate in hybridization.
• Orbitals having nearly same energy can undergo hybridization.

[Note : 2s and 2p orbitals of the same atom undergo hybridization but 3s and 2p orbitals of the same atom do not.] 

Bond order of a molecule = \(\frac{N_b-N_a}{2}\) 

Where,

N_b is the number of electrons present in bonding MOs and N_a is the number of electrons present in antibonding MOs.

The steps involved in hybridization are : 

• formation of the excited state and 
• mixing and recasting of orbitals.

Hybridization is defined as the process of mixing of valence orbitals of same atom and recasting them into equal number of new equivalent orbitals (hybrid orbitals).

The correct option is-(a) 3 4 1 2

The correct option is- (a) 4 1 2 3

The correct option is- (b) 2 4 1 3

The correct answer is- (a) I₃^-

The correct option is- (b) IO₂F₂^-

A covalent bond formed due to the overlapping of orbitals of the two atoms along the line joining the two nuclei (orbital axis) is called sigma (σ) bond. 

For example, the bond formed due to s-s and s-p, p-p overlapping along the orbital axis are sigma bonds.

A covalent bond formed by the side wise overlapping of p- or d orbitals of two atoms is called as pi (π) bond. 

For example, the bond formed due to the sideways overlapping of the two p- orbitals is a pi- bond.

The given structures cannot be taken as the canonical forms of the resonance hybrid of H₃PO₃ because the positions of the atoms have changed.

BO₃³⁻ does not show resonance.

The formula 1 and 2 do not describe the canonical forms of the resonance hybrid representing H₃PO₃ because

(i) Position of one of the H nuclei is different.

(ii) The number of bonding and non-bonding pairs is different.

S – Orbital does not show any preference for direction because it is spherically symmetrical.

(a) Y

(b) Z

(c) X

(i) Both atoms should have four or more electrons in their outermost shells, i.e., non-metals.

(ii) Both the atoms should have high electronegativity.

(iii) Both the atoms should have high electron affinity and high ionisation potential.

(iv) Electronegativity difference between the two atoms should be zero or negligible.

(v) The approach of the atoms towards one another should be accompanied by decrease of energy.

(a) Ionic compounds are formed as a result of transfer of one or more electrons from the atom of a metallic electropositive element to an atom of a non-metallic electronegative element. A polar covalent compound is the one in which there is an unequal distribution of electrons between the two atoms.

(b) Ionic compounds, made up of ions, are generally crystalline solids with high melting and boiling points. They are soluble in water and good conductors of electricity in aqueous solution and molten state. Covalent compounds, made up of molecules, can exist as soft solids or liquids or gases with low melting and boiling points. They are generally insoluble in water and poor conductors of electricity.

(c) Polar covalent compounds are formed between 2 non-metal atoms that have different electro negativities and therefore have unequal sharing of the bonded electron pair. Non-polar compounds are formed when two identical non-metals equally share electrons between them.