According to the modern theory of acid-base indicators, an indicator is typically a weak organic aci — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Indicators rely on the contrasting colours of their protonated and deprotonated states (Quinoid theory). They visually transition across a roughly 2-unit pH range centered around their $pK_a$ ($pK_{In} \pm 1$). At $pH = pK_{In}$, $[HIn] = [In^-]$, producing a mixed/intermediate colour. Statement D is false because adding a strong acid supplies $H^+$, which shifts the equilibrium $HIn \rightleftharpoons H^+ + In^-$ backward via the common ion effect, generating more unionized $HIn$, not $In^-$.