Question

An alkaline (NaOH) solution of a compound produces a yellow colored solution on addition of NaBO₃. The compound is

• A. Mn(OH)₂
• B. Pb(OH)₂
• C. Cr(OH)₃
• D. Fe(OH)₃

Answer 1

The Correct Option is C

The question pertains to identifying which compound produces a yellow-colored solution on reacting with an alkaline (NaOH) solution and NaBO₃. Let's analyze the given options one by one:

1. The compound Mn(OH)₂: In alkaline solutions, manganous hydroxide does not participate in a reaction with NaBO₃ to yield a yellow color. Therefore, this option is incorrect.
2. The compound Pb(OH)₂: Lead hydroxide in an alkaline environment also does not react with NaBO₃ to produce a yellow-colored solution. Thus, this option is incorrect.
3. The compound Cr(OH)₃: Chromium hydroxide, in the presence of excess NaOH, forms chromate ions (CrO₄^2-), which are yellow in color. The reaction with NaBO₃ enhances the formation of these chromate ions, confirming the yellow coloration, making Cr(OH)₃ the correct answer.
4. The compound Fe(OH)₃: Iron(III) hydroxide does not react with NaBO₃ to produce a yellow solution in alkaline conditions. Therefore, this option is incorrect.

From this analysis, it is evident that the correct answer is Cr(OH)₃. The chromate ions formed in alkaline conditions are responsible for the yellow coloration.