Question

A colourless salt changes to yellow on heating. Salt is also soluble in $NaOH$ as well as in dil. $HCl$. Salt can be :

• A. $FeO$
• B. $PbO$
• C. $ZnO$
• D. $CdO$

Answer 1

The correct option is C $ZnO$

The colourless salt is zinc oxide.
At room temperature it is colourless but at high temperature, it becomes yellow. The change in colour is due to defects in the solid structure which increases with temperature. Zinc oxide is amphoteric in nature and is soluble in dil HCl as well as in NaOH.
$ZnO+2HCl\to ZnC{l}_2+H_{2}O$
$ZnO+2NaOH\to N{a}_{2}Zn{O}_2\left(sodiumzincate\right)+H_{2}O$