Question

The elements whose oxides can turn phenolphthalein solution pink are:

• A. $Na$ and $K$
• B. $K$ and $C$
• C. $Na$ and $S$
• D. $K$ and $P$

Answer 1

Answer: (A)

$Na$ and $K$

Phenolphthalein is a synthetic indicator which remains colourless in acidic and neutral medium but changes it's colour to pink in the basic medium.

Metal oxides are basic in nature and hence when phenolphthalein is added, the solution will change it's colour to pink, indicating that it is a base.

Na and K are alkali metals so their oxides are basic in nature whereas C,S and P are non-metals and hence their oxides will be acidic.

Thus, the correct answer is option (A).