12th Standard Chemistry March 2026: Online Practice Test

Explanation. Sodium is a highly electropositive metal that cannot be reduced by carbon, so it is extracted by electrolysis of fused NaCl (Down's process). Iron and lead are obtained by carbon reduction and silver by cyanide leaching.

Explanation. Down group 13 the inert pair effect increases, so the ns² electrons are less readily used in bonding. Hence the stability of the +1 state increases Al < Ga < In < Tl.

Explanation. Partial hydrolysis gives XeOF₄ and XeO₂F₂, but complete hydrolysis gives xenon trioxide: XeF₆ + 3H₂O → XeO₃ + 6HF.

Explanation. Co³⁺ and Fe²⁺ are both 3d⁶ with 4 unpaired electrons, silver is the best conductor, and the 15% rule (Hume-Rothery) applies to substitutional alloys, so (a)-(c) are correct. A metal with a large negative E° loses electrons easily and is a powerful reducing agent, not an oxidising agent, so (d) is incorrect.

Explanation. Pt(II) complexes are square planar. A complex of type [Mabcd] has three geometrical isomers, depending on which ligand is trans to a chosen ligand (e.g. Py trans to NH₃, Br or Cl).

Explanation. In Frenkel defect a cation only moves from its lattice site to an interstitial site; no ion leaves the crystal, so the density does not change. Both the assertion and the reason are false (loss of cation-anion pairs is Schottky defect).

Explanation. Number of half-lives n = 560/140 = 4. Amount left = 1 g × (1/2)⁴ = 1/16 g.

Explanation. Sodium formate is a salt of a weak acid and a strong base; its hydrolysis gives a basic solution with pH = 7 + ½pKa + ½log C.

Explanation. Λm = κ × 1000 / C = (5.76 × 10⁻³ S cm⁻¹ × 1000 cm³ dm⁻³) / 0.5 mol dm⁻³ = 11.52 S cm² mol⁻¹.

Explanation. By the Hardy–Schulze rule, only an ion with charge opposite to that of the colloidal particles causes coagulation (sign), and its coagulating power increases with the magnitude of its charge.

Explanation. Lucas reagent replaces the –OH group by –Cl without changing the carbon skeleton: CH₃CH(OH)CH₃ + HCl → CH₃CHClCH₃ (2-chloropropane) + H₂O.

Explanation. Reductive ozonolysis of ethene gives two molecules of formaldehyde (X). Formaldehyde condenses with ammonia: 6HCHO + 4NH₃ → (CH₂)₆N₄ (hexamethylene tetramine, urotropine) + 6H₂O.

Explanation. Sn/HCl reduces nitrobenzene to aniline (A); diazotisation at 273 K gives benzene diazonium chloride (B); warming with water at 283 K hydrolyses it to phenol (C), C₆H₅OH.

Explanation. α- and β-D-glucose differ only in the configuration at C-1, the anomeric (hemiacetal) carbon of the cyclic form, so they are anomers.

Explanation. Antagonists bind to the receptor site and block its natural function, whereas agonists mimic the natural messenger and activate the receptor.