Cassiterite is concentrated by

In the froth flotation process for the concentration of ores,why do the ore particles float?

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:

An ore of tin containing $FeCrO_4$ is concentrated by

Given below are two statements :
Statement $I :$ Sphalerite is a sulphide ore of zinc and copper glance is a sulphide ore of copper.
Statement $II :$ It is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants' in a froth flotation method.
Choose the most appropriate answer from the options given below :

In the cyanide process for extraction of gold and silver from ores,the cyanide solution acts as a