Chemistry 2021 Jamb Examination

Reduction is the chemical process that involves the gain of electrons by an atom, ion, or molecule.
It often occurs simultaneously with oxidation, which involves the loss of electrons.
During reduction, the oxidation state of the species decreases, meaning it becomes more negatively charged or less positive.
For example, when copper(II) ions gain two electrons, they are reduced to copper metal: \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \).

Redox reactions are those in which oxidation and reduction occur simultaneously.
In these reactions, one substance loses electrons (oxidised), while another gains electrons (reduced).
An example is the reaction between hydrogen and oxygen: \( 2H_2 + O_2 \rightarrow 2H_2O \).
Here, hydrogen is oxidised and oxygen is reduced, hence a redox process.

A binary compound of oxygen with another element is called an oxide.
Oxides are formed when oxygen combines with metals or non-metals.
Examples include water (H₂O), which is a non-metal oxide, and magnesium oxide (MgO), which is a metal oxide.
Oxides can be acidic, basic, or amphoteric depending on the element they combine with.

Metallurgy is the branch of science and technology that deals with the extraction of metals from their ores and their purification.
It involves various stages such as concentration of the ore, reduction, and refining.
For instance, iron is extracted from its ore haematite through a blast furnace process, which is a metallurgical operation.

Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms.
They are classified into alkanes, alkenes, and alkynes based on the type of bonds present.
Hydrocarbons are the main components of fossil fuels such as petrol and natural gas.
For example, methane (CH₄) is the simplest hydrocarbon.

Monosaccharides are simple sugars that exhibit physical properties such as being water-soluble and sweet-tasting.
They can be reduced to sugar alcohols, and when heated, they may char due to dehydration.
However, being vital to the exploration of metals is not a physical property of monosaccharides, making option C incorrect.

The troposphere contains two major types of pollutants: gaseous and particulate pollutants.
Gaseous pollutants include carbon monoxide, sulphur dioxide, and nitrogen oxides.
Particulate pollutants consist of dust, smoke, soot, and aerosols.
Both types contribute to air pollution and can have harmful environmental and health effects.

Ionisation enthalpy is the energy change that occurs when an electron is removed from an atom or ion in the gaseous state.
It is always a positive value because energy is required to overcome the attraction between the electron and the nucleus.
For example, \( \text{Na(g)} \rightarrow \text{Na}^+\text{(g)} + e^- \) involves ionisation enthalpy.

The fourteen elements following actinium in the periodic table (atomic numbers 90–103) are known as the actinoids or actinides.
They include thorium (Th), uranium (U), and plutonium (Pu).
These elements are typically radioactive and belong to the f-block of the periodic table.
They are important in nuclear chemistry and energy generation.

Hydrolysis is a chemical process in which a salt reacts with water to form an acid or a base.
This reaction occurs when the ions of the salt interact with water molecules, leading to either acidic or basic solutions depending on the nature of the ions.
For example, ammonium chloride undergoes hydrolysis to produce an acidic solution.