Chemistry 2021 Jamb Examination

Carbon dioxide (CO₂) is a greenhouse gas that traps heat in the Earth's atmosphere, contributing to global warming. It is produced mainly from burning fossil fuels, deforestation, and various industrial processes.
Oxygen (O₂) and nitrogen (N₂) are major atmospheric gases but are not greenhouse gases. Helium (He) is an inert gas that does not absorb infrared radiation.

Kerosene is a hydrocarbon composed mainly of carbon and hydrogen atoms, meaning it does not contain oxygen in its molecular structure. It is a refined petroleum product used as fuel.
Soil, glass, and cement all contain oxygen in their chemical composition, either as oxides or silicates.

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state. Substances like camphor, naphthalene, and dry ice exhibit this property when exposed to air.
Evaporation involves liquid changing to gas, diffusion involves the mixing of particles, and radiation is energy transfer by electromagnetic waves.

The maximum number of electrons in any shell is given by the formula \(2n^2\), where \(n\) is the shell number.
For the N shell, \(n = 4\):\[2n^2 = 2(4^2) = 2(16) = 32\]Therefore, the N shell can accommodate a maximum of 32 electrons.

James Chadwick discovered the neutron in 1932 through experiments involving the bombardment of beryllium with alpha particles. The neutron is a neutral subatomic particle found in the atomic nucleus.
Rutherford discovered the nucleus, J.J. Thomson discovered the electron, and John Dalton proposed the atomic theory.

All the listed substances — limestone, marble, chalk, and eggshells — are composed mainly of calcium carbonate (CaCO₃).
Limestone is a sedimentary rock, marble is its metamorphic form, chalk is a soft, porous form, and eggshells are biological structures also rich in CaCO₃.

Soaps work by reducing the surface tension of water, allowing it to spread and mix with oils and dirt more easily. This process enables the removal of greasy substances from surfaces.
The soap molecules have hydrophilic and hydrophobic ends that help form emulsions, making cleaning effective.

Fluorine is the most reactive non-metal due to its extremely high electronegativity and strong tendency to attract electrons. This makes it a powerful oxidising agent.
Its small atomic size enhances its reactivity. However, the F–F bond is actually weak, and fluorine lacks D-orbitals.

The mass number of a nucleus is the total number of protons and neutrons (nucleons) present in it.
It is always a whole number since it represents discrete particles, and it differs from the atomic number, which counts only protons.

One mole of helium atoms contains Avogadro's number (6.022 × 10²³) of atoms. The atomic mass of helium is 4 u, meaning one mole of helium atoms weighs 4 grams.
Hence, the mass of one Avogadro number of helium atoms is 4.00 grams.