Statement B is false because Sodium dichromate ($Na_2Cr_2O_7$) is hygroscopic (absorbs moisture from the atmosphere), making it difficult to weigh accurately for preparing standard solutions. Therefore, Potassium dichromate ($K_2Cr_2O_7$), which is not hygroscopic, is preferred as a primary standard in volumetric analysis .

Validating other options:

• Option A: Acidified $K_2Cr_2O_7$ is a strong oxidising agent and oxidises hydrogen sulphide ($H_2S$) to elemental sulphur ($S$), which renders the solution milky .
• Option C & D: Chromates ($CrO_4^{2-}$, yellow) and dichromates ($Cr_2O_7^{2-}$, orange) are interconvertible depending on pH. In acidic medium ($pH < 7$), the equilibrium favors dichromate (orange). In basic medium ($pH > 7$), the equilibrium shifts to chromate (yellow) .