** Radicals: ** A group of atoms forming an ion is called a radical. Such a radical or ion contains more than one atoms and hence are polyatomic in nature. There are two types of radicals, namely (a) Acid Radicals: –ve ions(anions). Many of them are derived from acids. (b) Basic Radicals : +ve ions(cations) They are derived from bases. ** Acids and Acid Radicals: ** The substances which can produce hydrogen ions(H+) in water or aqueous solution are called acids(Arrhenius Theory) $$1) \hspace{0.5cm} H_2SO_4 \Longrightarrow H^+ + HSO_4^{2–}$$ HSO~4~^–^ is the acid radical called hydrogen sulphate or bisulphate radical (ion), which is a polyatomic negative ion. Sulphuric acid (H~2~SO~4~) loses one H+ ion to form HSO~4~^–^ radical. $$H_2SO_4 \Longrightarrow 2H^+ + SO_4^{2–}$$ SO~4~^2–^ is called sulphate radical (ion). Sulfuric acid can lose two H^+^ ions to form SO~4~^2–^ ion. So H~2~SO~4~ can form two acid radicals namely HSO~4~^–^ and SO~4~^2–^. The