(a) Salt: NaCI is added while making soap, because it will cause precipitation of soap in solid form.
(b) In test tube A: Soap + Oil \(\longrightarrow\) Lather/foam is formed. Carbon chain of carboxylic salt dissolves in oil.
In test tube B: Soap + Hard water \(\longrightarrow\) Insoluble compound called scum is formed.
In test tube C: Soap + soft water \(\longrightarrow\) Froth is formed.
(c) Yes, we can use potassium hydroxide to prepare soap.

'X' is CH₃-CH₂OH ethanol. It can be made unsaturated by heating it with cone. H₂SO₄ which is a dehydrating agent and removes water from it, thereby forming ethene.
CH₃-CH₂OH \(\xrightarrow[{}{H_2SO_4}]{Hot \ Conc.}\) H₂C = CH₂ + H₂O
                          Ethene

Take ethanol in a test tube and drop a small piece of sodium about the size of a grain of rice into it. The reaction evolves a colourless gas which is hydrogen.
Hydrogen gas can be tested by bringing a burning splinter/matchstick near the mouth of the test tube, it bums with the popping sound.
This activity proves that ethanol like other acids release H₂ gas
2Na + 2CH₃CH₂OH \(\longrightarrow\) 2CH₃CH₂ONa + H₂

A is ethanol, C₂H₅OH
B is ethanoic acid, CH₃COOH
Equation: C₂H₅OH \(\overset {acidified \ K_2Cr_2O_7}{\longrightarrow}\) CH₃COOH

(i) A will have least number of carbon atoms.
(ii) C will have maximum number of carbon atoms.