Elements Compounds And Mixtures Quiz For Grade 7th

Na is the chemical symbol for sodium. Chemical symbols are used to represent elements in the periodic table, and Na specifically represents the element sodium. Sodium is a highly reactive metal that is commonly found in table salt and various other compounds. It is an essential element for many biological processes and is widely used in industry for various applications.

The chemical symbol for carbon is C. It is a nonmetallic element that is essential for life and is found in all living organisms. Carbon is known for its ability to form a wide variety of compounds, including organic compounds, and is a key element in many important molecules such as carbohydrates, proteins, and DNA. It is also a major component of fossil fuels like coal and oil.

An element is a pure substance made up of only one type of atom and cannot be separated into simpler substances by physical or chemical means. Elements are the basic building blocks of matter, and all other substances are made from combinations of elements. Therefore, the correct sentence is: "An element is a simple, pure substance. It cannot be separated."

Compounds are chemically combined because they are formed when two or more elements react with each other and bond together through chemical bonds. This chemical combination results in the formation of a new substance with different properties than the individual elements.

A mixture is composed of two or more substances that are combined together without being chemically reacted. Therefore, it can be separated because the substances in a mixture retain their individual properties and can be physically separated through methods such as filtration, distillation, or evaporation.

Carbon dioxide  (CO2) is not an element; it is a compound. An element is a substance that cannot be broken down into simpler substances by chemical means, while a compound is a substance made up of two or more different elements chemically bonded together. In the case of carbon dioxide, it is composed of one carbon atom bonded to two oxygen atoms. 

Mixtures are not chemically combined. A mixture is a combination of two or more substances that are physically mixed together but do not undergo any chemical reactions. The substances in a mixture can be separated by physical means, such as filtration or distillation, without changing their chemical properties. In contrast, chemical compounds are chemically combined, meaning their atoms are bonded together in a specific ratio, and they can only be separated by chemical reactions. 

Elements, compounds, and mixtures are not pure substances. Pure substances are defined as substances that are made up of only one type of particle, either atoms or molecules. Elements are pure substances because they are made up of only one type of atom. Compounds are also pure substances because they are made up of two or more different types of atoms bonded together. However, mixtures are not pure substances because they are made up of two or more different substances mixed together without any chemical bonding between them. 

An alloy is a mixture of two or more metals. It is formed by combining different metals together, typically to enhance their properties or create a material with specific characteristics. The metals in an alloy are evenly distributed, forming a solid solution. This differs from a compound, which is a substance formed by chemically bonding different elements together. Similarly, an alloy is not a solution of gases, as it specifically refers to a mixture of metals.

 It is possible to break down or divide a compound into its constituent elements or simpler compounds through various chemical or physical processes. This separation can be achieved by methods such as distillation, filtration, or chemical reactions.

The chemical symbol for Mercury is Hg because it comes from the Latin word "hydrargyrum" which means "liquid silver". The symbol Hg is derived from the Greek name for Mercury, "hydrargyros".

When ice melts, it absorbs heat from its surroundings in order to break the bonds holding its molecules together. This absorption of heat causes a decrease in temperature and is characteristic of an endothermic reaction. In an endothermic reaction, the system gains energy from the surroundings, resulting in a decrease in temperature.

Colloids are mixtures that do not settle out. Unlike suspensions, which have larger particles that eventually settle due to gravity, colloids have smaller particles that remain dispersed and do not settle. The particles in a colloid are evenly distributed throughout the mixture and are typically too small to be affected by gravity.

The given answer includes four methods that can speed up the process of dissolving. Stirring helps to increase the contact between the solute and solvent, allowing for faster dissolution. Boiling increases the temperature, which in turn increases the kinetic energy of the particles, leading to faster dissolving. Heating also raises the temperature, accelerating the movement of particles and enhancing the dissolving process. Crushing the solute into smaller particles increases the surface area, facilitating faster dissolution.