RRB Group D 8-Dec-2013 Shift 1 Solved Paper

The term ‘common alum’ is usually used in reference to potassium alum, which is the hydrated form of potassium aluminium sulphate and has the chemical formula KAl(SO4)2·12H2O.
Potassium alum is commonly used for household purposes. It is also the one that is most commonly referred to as alum. It is an inorganic salt.