Question

Which of the following oxides gives pink colour with phenolphthalein indicator in aqueous solution?

• A. $N_{2}O$
• B. $NO$
• C. $CaO$
• D. $C{O}_2$

Answer 1

Answer: (C)

$CaO$

$CaO$ gives pink colour with phenolphthalein indicator in aqueous solution.
An aqueous solution of $CaO$ is alkaline in nature due to hydrolysis.
$CaO+H_{2}O\to Ca(OH{)}_2+15000cal$
The phenolphthalein indicator is colourless in acidic medium and pink coloured in alkaline medium.
The aqueous solutions of $N_{2}O$ and NO are neutral.
The aqueous solution of $C{O}_2$ is acidic in nature.
$C{O}_2+H_{2}O\rightleftharpoons \underset{\text{carbonic acid}}{H_{2}C{O}_3}$