1.

Identify A

Answer»

ZnS
ZnO
MgO
FeO

Solution :Zinc OXIDE turns yellow on heating and white on cooling. (A) is `ZnO`, which is not soluble in water. `ZnO` is called Chinese white, zincite, philosopher's wool.
`ZnO +2HCI rarr UNDERSET((B))(ZnCI_(2)) +H_(2)O`
`ZnO +2NaOH rarr underset((C))(Na_(2)ZnO_(2))+H_(2)O`
`ZnO` is AMPHOTERIC.
`underset((B))(ZnCI_(2))+H_(2)S rarr` No ppt.
This is because `ZnS` is precipitated in basic medium with SUFFICIENT `[S^(2-)]` concentration.
`underset(("Neutral or basic solution"))(ZnCI_(2)+H_(2)S) OVERSET(NH_(4)OH)rarr underset((D))(ZnSdarr) +2HCI`


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