Class 12 NEET Chemistry D And F Block Elements Questions

Concept: Properties of potassium dichromate ($K_2Cr_2O_7$) and sodium dichromate ($Na_2Cr_2O_7$) in volumetric analysis.Explanation:$K_2Cr_2O_7$ is preferred over $Na_2Cr_2O_7$ in volumetric analysis. This is because $Na_2Cr_2O_7$ is highly deliquescent (it absorbs moisture from the atmosphere), making it difficult to weigh accurately to prepare a standard solution. On the other hand, $K_2Cr_2O_7$ is non-deliquescent and acts as an excellent primary standard. Therefore, the statement that $Na_2Cr_2O_7$ is preferred over $K_2Cr_2O_7$ is incorrect.Other statements are correct:

• Acidified $K_2Cr_2O_7$ oxidizes $H_2S$ to elemental sulfur, giving a milky appearance.
• $K_2Cr_2O_7$ is orange in an acidic medium ($Cr_2O_7^{2-}$).
• It turns yellow in a basic medium (pH > 7) due to the formation of chromate ions ($CrO_4^{2-}$).

Answer: Option B