Which of the following is used as froth stabilizer in froth floatation process?

White phosphorus on heating with concentrated NaOH solution in an inert atmosphere of $\mathrm{CO}_2$ gives a salt ' $X$ ' and gas ' $Y$ '. The oxidation state of central atom in $X$ and $Y$ is respectively

For which of the following the $E^{\ominus}\left(M^{3+} / M^{2+}\right)$ is negative?

In $\mathrm{Fe}_x\left[\mathrm{Fe}_y(\mathrm{CN})_6\right]_3, x, y$ respectively, are