Chemistry 2025 Jamb Examination

The chemical equation shows the substance dissociating into discrete positive ions (Na⁺) and negative ions (X^2-) when in solution. This behaviour is characteristic of ionic compounds, which are formed by the electrostatic attraction between oppositely charged ions. Since Sodium (Na) is a metal and X is acting as a non-metal anion, the bond is established through the transfer of electrons rather than sharing.

Alkanoates, commonly known as esters, are organic compounds formed by the reaction between an alkanol and an alkanoic acid. They are well known for their distinct, often sweet and fruity fragrances. Many natural flavours in fruits like pineapples, bananas, and oranges are caused by specific esters, and they are synthesized industrially for use in perfumes and artificial flavourings.

Ethanedioic acid (oxalic acid) is a weak organic acid, while potassium hydroxide (KOH) is a strong base. In a titration between a weak acid and a strong base, the equivalence point occurs at a pH greater than 7 (basic). Phenolphthalein is the most suitable indicator because its colour change interval (pH 8.2 to 10.0) matches the expected basic pH at the endpoint of this specific reaction.

Chlorine has an atomic number of 17, which means a neutral atom has 17 electrons. Following the Aufbau principle, these electrons fill the orbitals in order of increasing energy: 1s (2), 2s (2), 2p (6), 3s (2), and 3p (5). Summing these gives 2 + 2 + 6 + 2 + 5 = 17. Option A correctly represents this ground-state configuration.

The electrochemical series (or activity series) is a list of elements, primarily metals, arranged in order of their standard electrode potentials or their reactivity. In this series, metals are ranked based on how easily they undergo oxidation (lose their valence electrons) to form positive ions. Metals at the top of the series lose electrons more readily than those at the bottom.

By definition, solubility refers to the maximum quantity of a substance (solute) that can dissolve in a specific volume of solvent at a given temperature and pressure to form a saturated solution. While dissolving a solute can affect vapour pressure or boiling point (colligative properties), the fundamental importance and definition of solubility itself lie in determining the capacity of the solvent to hold the solute.

For a first-order reaction, the relationship between the rate constant (\(k\)) and the half-life (\(t_{1/2}\)) is given by the formula:\[t_{1/2} = \frac{0.693}{k}\]Substituting the given value of \(k = 3.85 \times 10^{-3} \, \text{s}^{-1}\):\[t_{1/2} = \frac{0.693}{0.00385} = 180 \, \text{s}\]The time taken for half of the radioactive phosphorus to decay is 180 seconds.

The structure RCONH₂ contains a carbonyl group (C=O) bonded directly to a nitrogen atom (NH₂). This specific functional group, CONH₂, is characteristic of an amide. In the general naming convention for this class of organic compounds, they are known as alkanamides. 

Alkylamine: Amines have a general formula of RNH₂ (primary amine) without the carbonyl group (C=O) adjacent to the nitrogen.

Alkanone: Alkanones, also known as ketones, have a carbonyl group (C=O) bonded to two other carbon atoms (RCOR'), and do not contain a nitrogen atom.

Amino acid: Amino acids are organic compounds that contain both an amino group (–NH₂) and a carboxylic acid group (–COOH) attached to the same central carbon atom, along with a hydrogen atom and a variable side chain (R group). The structure RCONH₂ lacks a carboxyl group. 

Crude oil is a complex mixture of hydrocarbons with different boiling points. In an oil refinery, these components are separated on a large scale using fractional distillation. This process involves heating the crude oil and allowing the vapours to rise up a fractionating column; the different components (fractions) condense at different heights based on their specific boiling ranges.

The equilibrium constant expression, based on the law of mass action, is defined as the ratio of the concentrations of the products raised to their stoichiometric coefficients to the concentrations of the reactants raised to their stoichiometric coefficients.

The correct answer is option D -  \(\frac{[X_2][Y_2]^3}{[XY_3]^2}\)