**2. Chemistry of arsenic**

In the natural environment, arsenic shows diverse chemical behavior. Arsenic has the potential to readily change oxidation state and bonding configuration, producing inorganic and organic forms [9]. In the periodic table, arsenic is in the 33rd position of the periodic table, secures a position in Group 15, being a member of the nitrogen family. The atomic number of arsenic is 33 and its atomic weight is 74.921, thus it is heavier than iron, nickel, and manganese but lighter than silver, lead or gold. The electronic configuration of the stable form of arsenic, As (0) is: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3 . There exist four oxidation states of arsenic *viz.* arsines and methyl arsines, elemental arsenic, arsenite, and arsenate, the inorganic form of arsenic is highly lethal and mobile in the atmosphere compared to the organic form. Arsenite is found to be 10 times more poisonous than arsenate [10].

## **3. Global scenario of arsenic contamination**

Arsenic is a matter of global concern because of its adverse health effects. Arsenic is widespread at a high concentration in the groundwater throughout the world: Asia (Bangladesh, China, India, Inner Mongolia, and Taiwan), Europe (Hungary), and the Americas *viz.* Argentina, Chile, Mexico, and the northeast and western United States of America [2]. It was reported that about 150 million people across the world were affected by arsenic and the number is increasing as newly affected areas are discovered continuously [11]. In 2019, the number of affected people has increased to 500 million around the globe [12].
