Phenolpthalin and methyl orange are called as ________ which change the colour from acidity to alkalinity or vice versa.

Phenolphthalein (misspelled as 'Phenolpthalin') and methyl orange are pH indicators that change color depending on acidity or alkalinity. Phenolphthalein is colorless in acid and pink in base, while methyl orange is red in acid and yellow in base. Catalysts, electrolytes, and enzymes are different types of chemical substances.