What is concentration of ore?

The substance added in water in the froth floatation process is

Cassiterite is concentrated by

In the leaching method,bauxite ore is digested with a concentrated solution of $NaOH$ that produces $X$. When $CO_2$ gas is passed through the aqueous solution of $X$,a hydrated compound $Y$ is precipitated. $X$ and $Y$ respectively are

Observe the following statements regarding the purification of bauxite:
$I$. During Hall's process,silica is removed as $Si$ (vapour).
$II$. Bauxite ore contaminated with $Fe_2O_3$ is purified in Baeyer's process.
$III$. During Serpeck's process,$AlN$ is formed.
The correct answer is:

Which of the following statements is not correct?
$(i)$ Froth-floatation is used for removing gangue from sulphide ore.
$(ii)$ Cresols are used to stabilise the froth.
$(iii)$ Sodium cyanide can be used as depressant for preferential separation.
$(iv)$ Aniline can be used as froth enhancer.