Answer:
a. precipitation
Explanation:
In the reaction:
Ni²⁺(aq) + 2NaOH(aq)→ Ni(OH)₂(s) + 2 Na⁺
Nickel is precipitated as Ni(OH)₂ producing Na⁺ ions.
In a precipitation two soluble ions react with each other to produce an insoluble salt.
In our problem, Ni²⁺ is reacting with OH⁻ to produce Ni(OH)₂, an insoluble salt
The reaction is a precipitation
In an acid-base reaction, an acid reacts with a base to produce water and a salt. In this problem is a base reacting (NaOH) but there are no acids in the reaction.
And in a redox reaction an ion is been oxidized whereas the other is been reduced (Loosing electrons and gaining electrons).
As you can see, Ni²⁺ still with oxidation number of 2+ in Ni(OH)₂ and Na⁺ is always +1-. Thus, this is not a redox reaction.
