Identify the correct statements among the following.
I) Both $Cr$ and $Cu$ show +1 oxidation state
II) The complementary color of absorbed green color of visible radiation is purple.
III) ${\mathrm{Ni}}^{+2}$ ion in its hydrated state exhibits green color
IV) Brass is an alloy of copper and $Zn$

Given:- It is given to find the correct statements.

Explanation:-

1) $\mathrm{Cr} \mathrm{and} \mathrm{Cu}$ both have same $4s^1$ electronic configuration but +1 state of $\mathrm{Cr}$ is a less stable, mainly it shows +2, +3 and +6 state.

2) Purple color of emitted ray is complementary to the green color of absorption radiation.

3) ${\mathrm{Ni}}^{+2}$ion in hydrated state exhibits green colour.

4) Brass is an alloy of copper and zinc.