Answer:
Ammonium chloride
Step-by-step explanation:
The powder is:- Ammonium chloride
When mixed with silver nitrate, white prescipitate of silver chloride is formed as:-

When mixed with sodium hydroxide, ammonia gas is formed which has noxious order.

Ammonia gas on reaction with nickel (II) hydroxide forms deep blue colored complex as shown below:-
![Ni(OH)_2(s) + 6NH_3(aq)\rightarrow [Ni(NH_3)_6]^(2+)(aq) + 2OH^(-)(aq)](https://img.qammunity.org/2020/formulas/chemistry/high-school/4gqa8jvqzpb77r7aks6u2i0rhxrwdcexqp.png)