Which of the following units of electrical measurement is not equivalent to 1 Siemen?

What is the oxidation number of carbon in $\mathrm{K}_2 \mathrm{C}_2 \mathrm{O}_4 ?$

What type of isomerism is exhibited by $\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{Cl}_3$ and $\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_5 \mathrm{Cl}\right] \mathrm{Cl}_2 \cdot \mathrm{H}_2 \mathrm{O}$

Which of the following groups exhibits (+)R effect?