An indicator ‘X’ is used for studying the effect of variation in concentration of iodide on the rate of reaction of iodide ion with at room temperature. The indicator ‘X’ forms blue colored complex with compound ‘A’ present in the solution. The indicator ‘X’ and compound ‘A’ respectively are:
Starch and iodine
Methyl orange and
Starch and
Methyl orange and iodine
Correct answer:B
Standard Method
Given: The reaction involves iodide ion and at room temperature, and indicator ‘X’ forms a blue colored complex with compound ‘A’ present in the solution.
Find: The identities of indicator ‘X’ and compound ‘A’.
In this reaction, iodine is produced as a product when reacts with . Starch is commonly used as an indicator because it forms a blue-colored complex with iodine.
Thus, the indicator is starch, and the compound forming the blue complex is iodine. The solution states the correct option is B.
Assuming that itself gives the blue colour is incorrect, because the blue complex is formed specifically between starch and iodine. Identify the product formed first, then match the indicator behaviour.
Confusing methyl orange with starch is incorrect, because methyl orange is an acid-base indicator and does not form the characteristic blue complex in this reaction. Use the known starch-iodine test instead.
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