Chemistry 2025 Jamb Examination

A diagonal relationship occurs between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These pairs, such as Lithium/Magnesium, Beryllium/Aluminium, and Boron/Silicon, show similar chemical properties due to comparable ionic sizes and charge densities. Looking at the options, Boron (B) and Silicon (Si) share such a relationship, as do Beryllium and Aluminium (not listed correctly in pair C). Therefore, B and Si is the accurate pair among the choices provided.

Water pollutants are substances or conditions that degrade water quality. Warm water affluent causes thermal pollution, inorganic fertilisers lead to eutrophication, and biodegradable waste consumes dissolved oxygen during decomposition. Oxygen gas, however, is a vital natural component of water necessary for the survival of aquatic organisms. Increasing the dissolved oxygen content generally indicates better water quality rather than pollution.

Acid radicals, also known as anions, are the negatively charged ions formed when an acid loses its hydrogen ions. Examples include the carbonate ion from carbonic acid, the sulphate ion from sulphuric acid, and the nitrate ion from nitric acid. Option C is the only set containing exclusively negatively charged acid radicals (\(CO_3^{2-}\), \(SO_4^{2-}\), and \(NO_3^{-}\)), whereas the other options include metallic cations like \(Mg^{2+}\), \(Na^{+}\), or \(K^{+}\).

While the covalent bonds holding atoms together within a molecule are very strong, the forces of attraction between separate molecules (intermolecular forces, such as Van der Waals forces) are relatively weak.
Because these intermolecular forces are easily overcome with a small amount of thermal energy, covalent molecular substances typically have low melting and boiling points compared to ionic or giant covalent structures.

The immediate product of the reduction of iron ore in a blast furnace is known as pig iron.
It contains about 3% to 4.5% carbon along with other impurities like silicon and phosphorus. When pig iron is remelted and cooled, it becomes cast iron. Wrought iron and steel are produced by further refining pig iron to reduce its carbon content.

The molecular mass (molar mass) of a substance is the mass of one mole of that substance. We can use the formula:\[ ext{Molar Mass} = \frac{\text{Mass}}{\text{Number of moles}}\]Given that 0.5 mole weighs 44g, we calculate:\[ ext{Molar Mass} = \frac{44 \text{ g}}{0.5 \text{ mol}} = 88 \text{ g/mol}\]The molecular mass of the alkanoic acid is therefore 88.

Alkenes are unsaturated hydrocarbons containing at least one carbon-to-carbon double bond. Their general molecular formula is \(C_nH_{2n}\). For example, ethene is \(C_2H_4\) and propene is \(C_3H_6\). In contrast, \(C_nH_{2n+2}\) represents alkanes, \(C_nH_{2n-2}\) represents alkynes, and \(C_nH_{2n+1}OH\) represents alkanols (alcohols).

This reaction follows Markovnikov's rule, which states that during the addition of a hydrogen halide to an asymmetric alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms already present.
In 2-methylpropene (\((CH_3)_2C=CH_2\)), the terminal carbon has two hydrogens while the central carbon has none. Therefore, the hydrogen from \(HCl\) adds to the terminal carbon, and the chlorine adds to the central carbon, forming 2-chloro-2-methylpropane (also known as tertiary butyl chloride).

Chlorine gas is typically prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide. During heating, some \(HCl\) gas escapes along with the chlorine.
The gas mixture is passed through a wash bottle containing water because hydrogen chloride gas is extremely soluble in water, whereas chlorine gas is only moderately soluble. This effectively removes the \(HCl\) impurity from the chlorine gas stream.

Fructose is a hexose sugar with the molecular formula \(C_6H_{12}O_6\). When expressed in the general hydrate-of-carbon formula \(C_x(H_2O)_y\), it becomes \(C_6(H_2O)_6\). In this representation, the value of \(x\) (the number of carbon atoms) is 6. This is consistent with its classification as a monosaccharide with six carbon atoms.