Question

Identify the tube(s) in which the colour of red litmus paper turns blue.

• A. Test tube A
• B. Test tube B
• C. Test tube C
• D. All of the above

Answer 1

The correct option is C Test tube C

We know that, red litmus paper turns blue in the presence of basic or alkaline medium.

• Test tube A contains common salt, $NaCl$ which is neutral. Thus, it doesn't change the colour of any litmus paper.
• Test tube B contains sugar which is also neutral. Thus, it doesn't change the colour of any litmus paper.
• Test tube C contains calcium oxide, $CaO$ which is a metal oxide. Metal oxides are basic oxides. Thus, it turns red litmus paper to blue.

Hence, option C is correct.