a) The method used for removing gangue from sulphide ores is [[1]].
b) Wrought iron differs from steel in that it's created as a process whereby liquid iron is mixed with slag in an environment designed to keep its carbon content [[1]].

a)  Gangue is the vein matter that contains the majority of the valuable metals or many minerals. The gangue removal process is based on the chemical and physical properties of the gangue.

The froth flotation process is used for the removal of gangue from sulphide ore. In this method, a frothy mixture of oil (pine oil) and water is created in the tank that separates the sulphide ores. Because of differences in their wetting properties, the gangue particles and ores separated.

Hence, the method used for removing gangue from sulphide ores is froth flotation process.

b) Wrought iron is made of iron. It contains very little carbon and is the purest form of iron, with very few impurities and no additives. Steel is made up of carbon as well as other elements.

In contrast to steel, wrought iron is produced using a process in which liquid iron is combined with slag in a setting intended to maintain a low carbon content. It's a delicate balance that requires years of practise and commitment to master. With too much carbon, iron loses its malleability and becomes brittle.

Hence, the answer is Froth flotation, low.