Given below are two statements:
Statement-I: Methyl orange is a weak acid.
Statement-II: The benzenoid form of methyl orange is more intense/deeply coloured than the quinonoid form.
In the light of the above statement, choose the most appropriate answer from the options given below:

We recall that an acid-base indicator is itself a weak acid or a weak base which exists in two tautomeric/conjugate forms having different colours. Methyl orange behaves exactly in this manner.

Case 1: Nature of methyl orange
 • The indicator may be written as $$HIn$$ (acidic form) in equilibrium with its conjugate base $$In^-$$.
 • The dissociation equilibrium is $$HIn \rightleftharpoons H^{+}+In^{-}$$.
 • Since the position of this equilibrium changes with pH and methyl orange shows a pH range of about $$3.1$$ to $$4.4$$, the acid dissociation constant $$K_a$$ is small. Hence methyl orange is a weak acid.
Therefore Statement-I is correct.

Case 2: Colour of the two structural forms
 • In acidic solution the protonated (benzenoid) structure dominates and the colour observed is red.
 • In basic solution the de-protonated (quinonoid) structure dominates and the colour observed is yellow/orange.
 • Red is visually a deeper or more intense colour than yellow. Hence, for methyl orange, the benzenoid form is more intensely coloured than the quinonoid form.
Therefore Statement-II is also correct.

Because both statements are correct, the most appropriate choice is Option C.