A clear solution of bismuth nitrate in dilute nitric acid turns milky white when poured into a large volume of water. The responsible species and reaction is

Aoxidation of $Bi X^{3 +}$ to $Bi X^{5 +}$ giving white $Bi X_{2} O X_{5}$
Breduction of $Bi X^{3 +}$ to $Bi$ giving a white metal powder
Chydrolysis giving a basic salt, e.g. $Bi X^{3 +} + NO X_{3} X^{-} + H X_{2} O BiONO X_{3} + 2 H X^{+}$ (white)
Dformation of white $Bi (NO X_{3}) X_{5}$

Answer: C

Bi X^{3 +}

is strongly hydrolysed on dilution, depositing the basic salt

BiONO X_{3}

(with chloride,

BiOCl

). Adding acid reverses it by raising

[H X^{+}]

. No redox change occurs, and the metal would be black, not white.