Chemical Compounds and Reactions

Sodium thiosulphate (Na2S2O3) is commonly called 'hypo' in photography. It's used as a fixing agent to dissolve unexposed silver halide from photographic film or paper, making the image permanent.

It is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

Bleaching powder is chemically calcium oxychloride (CaOCl2), formed by passing chlorine gas over dry slaked lime (calcium hydroxide). It's widely used for disinfection and bleaching applications.

Photochromic glass contains silver halides (compounds of silver with chlorine, bromine, or iodine) that darken when exposed to UV light. Silver iodide is one such compound that undergoes a reversible chemical reaction, causing the darkening effect. Other options like alumina (aluminum oxide), lead oxide, and ferrous oxide do not have this photochromic property.

This option is correct because tetrammine copper (II) sulphate is called as Schweitzer's reagent. It dissolves cellulose and is therefore, used in the manufacture of rayon.

P. The central metal atom in potassium chromate and potassium dichromate is Cr. Chromium has +VI oxidation state in K₂CrO₄ and K₂Cr₂O₇. Q. Limonite (Fe₂O₃.3H₂O) is an ore of iron and willemite is an ore of zinc. R. Zinc oxide is an inorganic compound with the formula ZnO. ZnO is a white powder that is insoluble in water, and it is widely used as an additive in numerous materials and products including rubbers, plastics, ceramics, glass, cement, etc. White lead (PbCO₃).2Pb(OH)₂ is a complex chemical compound containing both a carbonate and a hydroxide portion and occurs naturally as a mineral for lead. White lead compounds were used as pigmenting materials like cement, lubricants, etc. but due to its toxicity, it is not used frequently.  Hence, both the statements Q and R are incorrect.

P. Iron (Fe) is used as a catalyst in the manufacture of ammonia by Haber process. CuCl₂ is used as catalyst in Deacon process for the preparation of Cl₂ from HCl. Q. CuCl in aqueous solution form Cu⁺ ions, which possess no colour due to the presence of completely filled d-orbitals. R. Zone melting is a group of techniques used to purify an element or a compound/metal or control its composition by melting a short region (i.e. zone) and causing this liquid zone to travel slowly through a relatively long ingot, or charge of the solid. As the zone travels, it redistributes impurities along the charge. The final distribution of the impurity depends on its distribution in the starting charge of material. This method is based on fractional crystallisation and so it is also called as zone-refining. Hence, both the statements P and Q are false.

When hydrogen chloride gas (from a chloride test) reacts with ammonia (often from an ammonia solution), it forms white fumes of solid ammonium chloride (NH4Cl).

Fe³⁺(aq): Yellow Mn³⁺(aq): Violet

Sc³⁺(aq), Ti⁴⁺(aq), Zn²⁺(aq) and Cd²⁺(aq): All are colourless due to lack of unpaired electrons.

Both Fe²⁺(aq) and Ni²⁺(aq) are green.

Red form of lead oxide is called litharge, and the yellow form is massicot.

Bleaching powder is chemically known as calcium hypochlorite, with the formula CaOCl2. It is widely used for disinfection and bleaching purposes.

Strontium salts produce red colors in fireworks, while barium salts produce green colors. These elements are standard components used in pyrotechnics to achieve specific color effects.

According to Hardy Schulze law greater is the valency of the coagulating or the flocculating ion, greater is its power to bring about coagulation. Hence, for the coagulation of negatively charged arsenious sulfide sol, trivalent cations (Al³⁺) are far more effective than divalent (Ba²⁺) cations.