Question

Some example of changes are given below. Classify them into:​ I: Irreversible physical change, II: Chemical change, ​ III: Reversible physical change ​

Answer 1

$\bullet$ When a fresh piece of brinjals is cut open, the chemical present in the brinjal reacts with the oxygen in the air. The reaction that occurs, is called oxidation, which in turns the vegetable brown. So, it is a chemical change.
$\bullet$ Rusting of iron is a chemical change that converts iron metal into a new substance known as rust.
$\bullet$ Making almirah from wood involves cutting of wood. Cutting wood into small blocks is an irreversible physical change.
$\bullet$ Melting of glaciers is a reversible physical change, in melting of glaciers only the state of water is changed from solid to liquid.
$\bullet$ Magnesium ribbon is the original substance and magnesium oxide is the final substance. Thus, on burning, the chemical composition changes. Hence, this is a chemical change.
$\bullet$ During crystallisation, there is no change in the chemical composition of a substance. Hence, this is a physical change.
$\bullet$ Breaking down ozone to oxygen is a chemical change as ozone and oxygen are two different substances having different physical and chemical properties.
$\bullet$ When carbon dioxide is passed through limewater, it turns milky due to a chemical change (chemical reaction).​
$\bullet$ Galvanization is a physical change since it deposits only a layer of zinc metal over the iron object.
$\bullet$ Food digestion is considered a chemical change because chemicals in the stomach and intestines break down large particles into simpler particles.
$\bullet$ Thus, option C is the right answer.