Correct solution of class 12 NCERT physics book

 

The given solution is wrong. 

My google query: work is done on the dipole, therefore there should be gain in its potential energy?

Following is the correct solution by google AI search:

What is a Redox Couple

 

why we take the electrolyte of the same substance?

Potential energy of a dipole in a uniform electric field

 

Function of Salt Bridge in a Voltaic cell

 Salt Bridge video

The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.

 Depression in freezing point is a colligative property that depends on the number of solute particles in a solution. Since the order of depression is 

Acetic acid < Trichloroacetic acid < Trifluoroacetic acid

It means the number of ions produced in the solution increases in the same order. 

This increase in ionization relates directly to the acidic strength of each acid: 

Trifluoroacetic acid (CF3COOH) has the strongest electron-withdrawing inductive effect due to the highly electronegative fluorine atoms, making it the strongest acid. It ionizes to the largest extent in water, producing the highest number of ions. 
Trichloroacetic acid (CCl3COOH) is weaker than the trifluoro derivative because chlorine is less electronegative than fluorine, resulting in a moderate degree of ionization. 
Acetic acid (CH3COOH) is the weakest acid because the methyl group (CH3) is electron-donating effect, which hinders ionization. It produces the fewest ions.

Because a greater degree of dissociation results in more solute particles, the depression in freezing point is maximum for trifluoroacetic acid and minimum for acetic acid.

Suggest the most important type of intermolecular attractive interaction in the following pairs. (i) n-hexane and n-octane (ii) 12 and CC14 (iii) NaCIO, and water (iv) methanol and acetone (v) acetonitrile (CH3CN) and acetone (C3H6O).

 Here are the most important types of intermolecular attractive interactions for each pair based on their molecular structures and polarities: 

(i) n-hexane and n-octane: Both are nonpolar hydrocarbons. The primary interaction is London dispersion forces.
(ii) (I2) and (CCl4: Both are nonpolar molecules. The primary interaction is London dispersion forces.
(iii) (NaClO4) and water: (NaClO4) is an ionic compound that dissociates into ions, and water is polar. The interaction is an ion-dipole interaction.
(iv) Methanol and acetone: Both are polar molecules, and methanol features a hydroxyl (-OH) group. The most important interaction is hydrogen bonding.
(v) Acetonitrile (CH3CN) and acetone (C3H6O): Both are polar molecules lacking (H) directly attached to highly electronegative atoms. The primary interaction is dipole-dipole interactions

Based on solute-solvent interactions, arrange the following in order of increasing solubility in n-octane and explain. Cyclohexane, KCI, CH3OH, CH3CN.

 The correct arrangement of the given compounds in order of increasing solubility in n-octane is:

KCl < CH3OH< CH3CN < Cyclohexane 

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Explanation based on Solute-Solvent Interactions

The rule governing solubility is "like dissolves like", which means polar/ionic solutes dissolve in polar solvents, and non-polar solutes dissolve in non-polar solvents.

Nature of Solvent: n-Octane (C8H18) is a long-chain hydrocarbon and is entirely non-polar.
Cyclohexane (Most Soluble): Like n-octane, cyclohexane (C6H12) is a non-polar hydrocarbon. The solute-solvent interactions involved are weak London dispersion forces. Because their natures are identical, they mix completely in all proportions.
(CH3CN) (Acetonitrile): It is a polar molecule due to the cyano (-CN) group, but it lacks the capability to form strong intermolecular hydrogen bonds. Therefore, it is less tightly held to itself than methanol and exhibits relatively better compatibility with the non-polar solvent.
(CH3OH) (Methanol): It is a highly polar molecule capable of strong intermolecular hydrogen bonding. Because breaking these hydrogen bonds to fit into a non-polar hydrocarbon solvent is energetically unfavorable, its solubility in n-octane is lower than that of acetonitrile.
KCl (Least Soluble): Potassium chloride is an ionic compound with high lattice energy. Since a non-polar solvent like n-octane cannot provide ion-dipole interactions to break the ionic lattice, KCl is virtually insoluble in it.