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The formula for water is H₂O. Water is a simple molecule composed of two hydrogen atoms (H₂) bonded to a single oxygen atom (O). The chemical formula H₂O represents the composition of water, indicating that it consists of two hydrogen atoms bonded to a single oxygen atom. Water is a fundamental and ubiquitous compound on Earth, essential for sustaining life and facilitating numerous biological, geological, and chemical processes.

The pH value of a neutral solution is 7. In the pH scale, values below 7 indicate acidity, while values above 7 indicate alkalinity. A pH of 7 signifies a perfectly balanced solution, where the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-). This balance between acidity and alkalinity is what defines a solution as neutral.

The chemical symbol for gold is Au. This symbol is derived from the Latin word "aurum," which means gold. Gold is a precious metal that is known for its lustrous yellow color and is often used in jewelry and as a form of currency. Its chemical symbol, Au, is used to represent gold in the periodic table of elements.

Helium is a noble gas because it belongs to the group 18 of the periodic table, also known as the noble gases or inert gases. Noble gases are characterized by having a full outer electron shell, making them stable and unreactive. Helium specifically has two electrons in its outer shell, fulfilling the octet rule. It is colorless, odorless, and has a low boiling and melting point, which makes it useful in various applications such as cryogenics, balloons, and as a protective gas in welding.

Carbon is the main component of organic compounds because it has the unique ability to form stable covalent bonds with other carbon atoms, as well as with other elements like hydrogen, oxygen, and nitrogen. This property allows carbon to form long chains and complex structures, which are the basis of organic compounds. Additionally, carbon has the ability to form double and triple bonds, further increasing the diversity and complexity of organic molecules. Therefore, carbon is considered the backbone of organic chemistry.

The atomic number of carbon is 6. The atomic number represents the number of protons found in the nucleus of an atom. Carbon atoms have six protons, which gives them an atomic number of 6. The atomic number is a fundamental property of an element and determines its position in the periodic table. Carbon is the sixth element in the periodic table, and its unique properties make it an essential building block of life on Earth.

A covalent bond involves the sharing of electrons between two atoms. In this type of bond, the atoms are able to fill their outermost electron shells by sharing electrons with each other. This sharing creates a stable electron configuration for both atoms, resulting in a strong bond. Covalent bonds are typically formed between nonmetals or between a nonmetal and a metalloid. Ionic bonds, on the other hand, involve the transfer of electrons, metallic bonds involve a sea of delocalized electrons, and hydrogen bonds are a type of intermolecular force.

Sublimation is the process that converts a solid directly into a gas. This occurs when the solid substance bypasses the liquid phase and goes straight from a solid to a gas. During sublimation, the particles of the solid gain enough energy to break the bonds holding them together and become a gas. An example of sublimation is dry ice (solid carbon dioxide) turning into gas when exposed to room temperature. Condensation, evaporation, and freezing involve different processes and do not directly convert a solid into a gas.

The SI unit for measuring temperature is Kelvin. Kelvin is the primary unit of temperature in the International System of Units (SI) and is commonly used in scientific and engineering applications. It is an absolute temperature scale where zero Kelvin represents absolute zero, the point at which all molecular motion ceases.

Nitrogen is the most abundant gas in Earth's atmosphere, accounting for about 78% of the total composition. It is present in a stable form and is essential for various biological and chemical processes. Oxygen, carbon dioxide, and hydrogen are also present in the atmosphere but in much smaller quantities compared to nitrogen.

While the Bohr model was groundbreaking for explaining the behavior of hydrogen, it has limitations. It doesn't accurately predict the spectra of larger atoms or explain the behavior of electrons in molecules. Modern atomic theory uses quantum mechanics to describe electron behavior, which is more complex than the fixed orbits proposed by Bohr.

Spontaneous processes tend to increase the entropy of the universe. This is because they lead to a greater dispersal of energy and matter. Entropy is a state function, meaning it depends only on the initial and final states of the system, not the path taken.

Methane has a tetrahedral geometry with four sigma bonds around the central carbon atom. To achieve this geometry, the carbon atom undergoes sp³ hybridization, where one s orbital and three p orbitals combine to form four equivalent sp³ hybrid orbitals. These orbitals then overlap with the 1s orbitals of the four hydrogen atoms to form the four C-H bonds.

Colligative properties depend on the number of solute particles in a solution, not their identity. Freezing point depression, boiling point elevation, and osmotic pressure all change based on solute concentration. Density, however, is an intrinsic property that depends on the mass and volume of the substance itself, not just the concentration of solute particles.

To determine the oxidation state of manganese (Mn), we assign -2 to each oxygen atom (a common rule). Since the overall charge of the ion is -1, the equation becomes: x + 4(-2) = -1, where 'x' is the oxidation state of Mn. Solving for x gives us +7.