The correct option is C KMnO4
In the presence of a reducing agent, KMnO4 acts as self-indicator and changes color from pink to colorless. Because in MnO−4 Mn is in +7 oxidation state and is in highest oxidation state. Thus will tend to get reduced and easily takes electrons and being a charge transfer complex, shows intense color. After titration it is MnO2 in +4 state and has no electronic charge transfer, therefore colorless.