Chemical Classification

Compounds are substances that are made up of two or more different elements chemically combined. This means that a compound must contain at least two elements in order to exist. Therefore, the statement "Compounds must contain at least two elements" is true.

This statement is true because compounds are made up of two or more elements that are chemically bonded together. These bonds can be broken through various chemical processes such as decomposition, oxidation, or hydrolysis, resulting in the formation of simpler substances. This breakdown allows for the release of energy and the rearrangement of atoms to form new compounds or elements.

Elements cannot be broken down further by processes such as boiling because elements are the simplest form of matter and are made up of only one type of atom. Boiling is a physical process that involves converting a substance from its liquid state to its gaseous state, but it does not break down the individual atoms that make up the element. Therefore, the statement is true.

A compound is not a physical mixture of simpler substances. A compound is a substance that is made up of two or more elements chemically combined in a fixed ratio. In a compound, the elements are chemically bonded together, resulting in a new substance with different properties than the individual elements. Therefore, the given statement is false.

Iodine, lead, and silicon are elements because they cannot be broken down into simpler substances by chemical reactions. Iodine is a halogen element, lead is a heavy metal element, and silicon is a metalloid element. Quartz, water, and silicone are not elements because they are compounds made up of two or more different elements.

The explanation for the given correct answer, which is False, is that elements are not pure substances, but rather the simplest form of matter that cannot be broken down further. Compounds, on the other hand, are pure substances composed of two or more elements chemically combined in fixed proportions. Therefore, elements are not mixtures, and compounds are not mixtures either.

Water and air are examples of matter because they both have mass and occupy space. Matter is anything that has mass and takes up space, and both water and air meet these criteria. Sound, heat, and energy, on the other hand, are not examples of matter because they do not have mass and do not occupy space.

Salt water and air (mostly N2 and O2) are both examples of mixtures. Salt water is a mixture because it is a combination of salt (NaCl) and water (H2O), where the salt dissolves in the water. Air is also a mixture because it consists of a combination of gases, primarily nitrogen (N2) and oxygen (O2), along with other trace gases. In both cases, the components of the mixture can be physically separated from each other.

Elements are pure substances that cannot be broken down by chemical means. They are the building blocks of matter and can combine chemically to form new substances.

Pure substances are defined as substances that are made up of only one type of atom or molecule. In the given list, table salt (NaCl), gold (Au), ethanol (CH3CH2OH), and elemental oxygen are all examples of pure substances. Table salt is composed of sodium (Na) and chlorine (Cl) atoms, gold consists of gold (Au) atoms, ethanol is made up of ethanol (CH3CH2OH) molecules, and elemental oxygen consists of oxygen (O2) molecules. These substances do not contain any impurities or other substances mixed in with them, making them pure substances.