Railway Science (Chemistry-Solutions)

When Ammonium hydroxide (NH₄OH) add into Aluminium Chloride (AlCl₃) , a white precipitate of Aluminium Hydroxide (Al(OH)₃ will be formed (under double displacement reaction).
Reaction: AlCl₃(aq) + 3NH₄OH(aq) → Al(OH)₃ (s) (white ppt) + 3 NH₄Cl (aq).
Aluminium Hydroxide has been used for relief of heartburn, sour stomach, and peptic ulcer pain.

Mg (Magnesium) is a metal that reacts with water to form magnesium hydroxide Mg(OH)₂ , which is basic in nature. Hence it turns the phenolphthalein solution pink.
Turmeric (natural indicator) - Turns red in presence of a base. Red cabbage (natural indicator)- Remains red in acidic solutions but turns green in the presence of a base.
Litmus - Acid turns blue litmus red and a base turns litmus blue. Methyl orange - Gives red color in an acid solution and yellow color in a basic solution.

In the question, the process executed is electrolysis, a process of chemical decomposition of the electrolyte by the passage of electric current. The breakdown of the electrolyte into ions is necessary for the flow of electricity. In options, all three solutions {like NaCl (Sodium Chloride) → Na⁺ (Sodium)+ Cl⁻ (Chlorine)} other than Octane can break into Ions. Hence, in the presence of Octane , the bulb does not glow.

Precipitate {insoluble substance, denoted by a downward arrow (↓)}. Chemical reaction - The process of one or more substances (reactants) combining and forming other substances (products).
That product is either in a solid, liquid, or gaseous state. Example - AgNO₃ (aq) + KCl (aq) → AgCl (↓) + KNO₃ (aq). In the above reaction, AgCl is a formed precipitate. An aqueous solution is a solution in which the solvent is water.

Zinc chloride (ZnCl₂) - Either white in colour or colourless, highly soluble in water. Ferric (III) iron hydroxide {Fe(OH)₃} - Used as an adsorbent to remove various heavy metals (Arsenic and chromium) from contaminated soil and water. Zinc Hydroxide {Zn(OH)₂ } - Odourless, Slightly soluble in water and insoluble in alcohol, Used in medicine as an adsorbing agent. Iron Chloride (FeCl₂) - Paramagnetic solid with a high melting point.

C𝑂₂ (carbon dioxide), CaC𝑂₃ (calcium  carbonate), Ca(HC𝑂₃)₂  (calcium   bicarbonate). When a piece of limestone reacts with dilute HCl, carbon dioxide (CO₂) gas is produced. When CO₂ gas is passed through lime water, a white precipitate calcium carbonate (CaCO₃) is formed.
On passing excess of CO₂ gas , the white precipitate dissolves, forming a soluble compound that is calcium hydrogen carbonate (calcium bicarbonate) Ca(HCO₃)₂ .

2Nacl (Sodium Chloride) + 2H₂O(l) → H₂(g) + Cl₂(g) + 2NaOH (Sodium Hydroxide). Cl₂ is produced at anode (positive electrode). H₂ and NaOH are produced at cathode (negative electrode).
Lime water / Calcium Hydroxide, Ca(OH)₂ . It is manufactured by the electrolysis of aqueous solution of sodium chloride (brine) in a Castner-kellner cell.

Copper (II) chloride (CuCl₂) aqueous solution is dark brown in colour, On dilution the colour changes to green and then blue because of successive replacement of chloride ions by water molecules.
Uses: oxidizing agent, purifying agent, mordant in dyeing, disinfectant, water treatment, manufacturing of agricultural chemicals.

Lead iodide (PbI₂) appears as a yellow crystalline solid, Insoluble in water and denser than water. It varies in colour from yellow to red, depending on the temperature. It is used in photography, printing, manufacturing solar cells, etc. Lead nitrate {Pb(NO₃)₂} - It is a white crystalline solid, Soluble in water, slightly soluble in ethanol.
It is noncombustible but it accelerates the burning of combustible materials. Melting Point - 470 °C. Sodium iodide (NaI) - It is a water-soluble ionic compound with a crystal lattice. It is odorless and colorless Cubic Crystals. Taste - Saline, Somewhat bitter in taste.

If the dispersed phase is a liquid and the dispersion medium is solid, the colloid is known as a gel. Examples - Cheese, butter, jellies etc. An emulsion is a mixture of two or more liquids that are normally immiscible owing to liquid-liquid phase separation. Examples - Milk, face cream, etc. Foam is a substance formed by trapping air or gas bubbles inside a solid or liquid. Example - Soap Suds etc.