Question

Which of the following is/are external indicators?
a.) Phenolphthalein
b.) Methyl orange
c.) Diphenylamine
d.) All of these.

Answer 1

Hint: Any substance or chemical that gives a visible mark, typically by a color change, of the presence or absence of a proper concentration of a chemical in the solution. An example of an indicator is EBT.
  Complete answer:
There are two types of indicators. Internal indicator and external indicator.
Some chemicals in the titration themselves act as indicators that are called as internal indicators. Potassium permanganate acts as an internal indicator.

Indicators that are added externally during the titration and wont act as reactants are known as an external indicator. Methyl orange is a best example of an external indicator.
Coming to the given options, option A, Phenolphthalein, it is an external indicator because we are going to add them separately in the chemical reaction. It is a correct option.
Coming to option B, methyl orange, it is also an external indicator because we are going to add them separately in the chemical reaction. It is also a correct option.
Coming to option C, diphenylamine, it is also an external indicator because we are going to add them separately in the chemical reaction. It is also a correct option.
Coming to option D, all of these.

All the three chemicals which are mentioned in the options (A, B, C) act as external indicators.

So, the correct option is option D.

Note: Phenolphthalein is colorless in acid medium and shows pink color in basic medium. Methyl orange is red in color in acidic medium and shows yellow color in basic medium. Diphenylamine is generally used in redox reactions to find the end point of the reaction.