Question

Three test tubes, labelled A, B, and C, contain different solutions. The results of dipping red and blue litmus papers in these test tubes are shown in the table below.

Analyse the table below and select the incorrect option from the following.
$\begin{array}{cccc}& \text{Test tube A}& \text{Test tube B}& \text{Test tube C}\\ \text{Red Litmus}& \text{No change}& \text{No change}& \text{No change}\\ \text{Blue Litmus}& \text{Red}& \text{No change}& \text{Red}\end{array}$

• A. The sample in test tube A is acidic
• B. The sample in test tube A is neutral
• C. The sample in test tube C is acidic
• D. The sample in test tube B is neutral

Answer 1

The correct option is B The sample in test tube A is neutral

Litmus paper is used to identify the nature of a solution. They are available in two colours- red and blue.
The following table shows the colour of each litmus in different medium:

$\begin{array}{cccc}& \text{Acidic}& \text{Neutral}& \text{Basic}\\ \text{Red Litmus}& \text{Red}& \text{Red}& \text{Blue}\\ \text{Blue Litmus}& \text{Red}& \text{Blue}& \text{Blue}\end{array}$

When a blue litmus paper was put in all these test tubes, it turned red in test tubes A and C. So, we can confirm that the samples in test tubes A and C are acidic.
No change in the colour of red litmus is observed when it is added to any of the test tubes. This marks the absence of a basic sample. Both litmus papers didn't change their colour when kept in test tube B. This means that the solution in test tube B is neutral.