Answer:
10
Step-by-step explanation:
The atomic number of Nickel is 28: this means that a neutral atom of nickel has 28 electrons.
The electronic configuration of nickel is:

abbreviated, this is written as
![[Ar]4 s^2 3d^8](https://img.qammunity.org/2020/formulas/physics/high-school/ocjg3wb1esidmka8kwokqqa0x9crrp99wc.png)
where
represents the electronic configuration of argon. This means that all the shells until
are completed, while the outermost shell:

is the one that gives us the number of valence electrons. Since there are 2 electrons in the 4s orbital and 8 electrons in the 3d orbital, the total number of valence electrons is
2 + 8 = 10