Which one of the following is the correct order of oxidation number of Iodine (I) in I2, HI, HIO4 and ICI?

The oxidation number of iodine (I) is determined by standard chemical rules. In its elemental form, I2, the oxidation number is 0 [t1][t5][t6]. In Hydrogen Iodide (HI), hydrogen is +1, making iodine -1 [t1][t2][t5]. In Iodine Monochloride (ICl), chlorine is more electronegative than iodine and is assigned -1, resulting in an oxidation state of +1 for iodine [t1]. In Periodic acid (HIO4), hydrogen is +1 and four oxygen atoms contribute -8 (4 x -2); to maintain neutrality, iodine must be +7 [t1][t2][t5][t9]. Comparing these values: HI (-1) < I2 (0) < ICl (+1) < HIO4 (+7). Therefore, the correct increasing order of oxidation numbers is HI < I2 < ICl < HIO4, which corresponds to option 2.