Test: Physical and Chemical Changes - Class 8 MCQ

The growth of a child is a slow change that occurs over many years, reflecting gradual physical and biological development. In contrast, the melting of ice, burning of paper, and boiling of water happen relatively quickly.

Periodic changes are those that occur at regular intervals, such as the change of seasons or the rising and setting of the sun. This predictability is what defines them as periodic, distinguishing them from non-periodic changes.

Baking a cake is an irreversible change because once the ingredients are mixed and baked, they cannot be returned to their original states. This process creates new substances with different properties, unlike physical changes which can be reversed.

Breaking a glass occurs very quickly and is considered a fast change. In contrast, processes like rusting and growth take much longer to happen, while the curdling of milk, although not immediate, is also relatively quicker than the other examples.

The melting of an ice cube is classified as a physical change because only the state of the matter changes from solid to liquid, and it can easily revert back to ice when cooled. This transformation does not produce any new substance.

A chemical change is characterized by a transformation in the internal composition of a substance, resulting in new substances being formed. These changes are typically permanent and cannot be reversed easily.

The rotation of the Earth is a natural change that occurs without human intervention, contributing to the cycle of day and night. In contrast, cooking food and making furniture are man-made changes.

Physical changes generally allow the material to return to its original state, meaning they are typically reversible. Examples include melting and boiling, where the original material can be recovered.

The main difference is that chemical changes produce new substances with different properties, while physical changes do not alter the original substance's composition and often allow for the original material to be recovered.

Fermentation is the process in which microorganisms, such as yeast or bacteria, convert sugars into different substances, often producing alcohol or acid. This process is a chemical change and results in new products that cannot revert to their original forms.

Rusting is a chemical change that creates a new substance (rust) with different properties from iron. This process is irreversible, meaning the original metal cannot be restored without significant effort.

Air pollution is considered an undesirable change because it negatively affects health and the environment. In contrast, ripening fruits and digestion are beneficial processes, while boiling water is a neutral physical change.

Melting chocolate is a physical change because it can be solidified again by cooling, thus reversing the process. In contrast, burning wood and baking bread are irreversible chemical changes.

The changing of seasons is a periodic change because it occurs at regular intervals throughout the year. This predictability distinguishes it from non-periodic changes, which do not follow a set schedule.

Sublimation is classified as a physical change because it involves a solid transitioning directly into a gas without passing through the liquid state. This process is reversible, allowing camphor to return to its solid form when cooled.