Question

What do you mean by colour cahang during chemical reaction

Answer 1

A chemical reaction isn't always visible to the human eye, but sometimes it results in an impressive color change and makes science experiments more fun to witness. When two or more substances combine, they create one or more new substances, which sometimes have different molecular structures from the original substances, meaning they absorb and radiate light in different ways, leading to a color change.

colour change also occurs due to addition of indicators.
Phenolphthalein is a universal indicator, which means it changes color to show the pH of certain solutions. Phenolphthalein stays colorless in acidic solutions and turns pink in alkaline solutions. Sodium hydroxide is a base, so when you add phenolphthalein, the solution turns pink. Other indicators commonly used in the laboratory are litmus and methyl orange.