The water cycle (basic)

Water on Earth is in a continuous state of change. The water cycle includes processes such as evaporation, precipitation, melting and freezing.

Folding (intermediate)

Lateral compressive forces cause rocks to form folds. This is how fold mountains are formed.

Battle of Varna (1444)

Hungarian King Władysław I died in the lost battle fought against the Ottomans.

Construction of a panel building

Buildings constructed of prefabricated concrete blocks were widespread in the former Socialist countries.

Hypochlorite ion (OCl⁻)

Hypochlorite ions are formed when water is disinfected with chlorine.

Amylose ((C₆H₁₀O₅)n)

A helical molecule consisting of alpha-D-glucose units. It is one of the basic components of starch.

Fibroin

Fibroin is a fibrillar protein excreted by silkworms.

Alpha-D-glucose (C₆H₁₂O₆)

Alpha-D-glucose is one of the stereoisomers of glucoses, specifically the D-glucoses.

Sulphuric acid (H₂SO₄)

A colourless, viscous liquid, a highly corrosive, strong acid used in several industrial processes.

Permanganate ion (MnO₄⁻)

Potassium permanganate is used as a disinfectant.

Silver iodide (AgI)

A light yellow compound formed in the reaction of silver nitrate and potassium iodide.

Sodium chloride (NaCl)

Common salt (or table salt) is one of the most important sodium compounds, indispensable for living organisms.

Silver bromide (AgBr)

A white, crystalline compound which breaks down when exposed to light.

Carbon monoxide (CO) (beginner)

Colourless, odourless gas, highly toxic to humans and animals in high concentration.

Pyrimidine (C₄H₄N₂)

A heterocyclic organic compound, its derivatives are thymine, cytosine and uracil.

Carbon dioxide (CO₂) (beginner)

Colourless, odourless, heavier-than-air gas. Necessary for the photosynthesis of plants.

Nitrogen (N₂) (basic)

A colourless, odourless, non-reactive gas, it constitutes 78.1% of Earth´s atmosphere.

Oxygen (O₂) (beginner)

A colourless, odourless gas, an important component of the atmosphere, indispensable to sustain terrestrial life.

Glyceraldehyde (C₃H₆O₃)

The simplest aldose, an optically active compound.

Comparison of halogens

Halogen elements are a group in the periodic table consisting of five chemically related elements, fluorine, chlorine, bromine, iodine, and astatine.

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