Identify the correct statements from the following.

(i) Ti (IV) is more stable than Ti (III) and Ti (II).

(ii) Among $3 d$-series elements (From $Z=22$ to 29). Only copper has positive reduction potential $\left(M^{2+} / M\right)$.

(iii) Both Sc and Zn exhibit +1 oxidation state.

The number $f$-electrons in +3 oxidation state of gadolinium $(Z=64)$ is $x$ and in +2 oxidation state of ytterbium $(Z=70)$ is $y$. The sum of $x$ and $y$ is