The Highest Value of Oxidation Number Changes from 1 to 7



Explanation:

Introduction:
The oxidation number is a concept used in chemistry to represent the charge that an atom has when it gains or loses electrons during a chemical reaction. It is a convenient way to keep track of the electron transfer in a reaction.

Understanding Oxidation Number:
The oxidation number can be positive, negative, or zero. It is usually written as a superscript or a subscript to the right of the element symbol. The highest value of the oxidation number depends on the element and its position in the periodic table.

Analysis of Options:
a) In the atoms of transition elements:
Transition elements are known for their ability to exhibit multiple oxidation states. They have partially filled d-orbitals, which allow them to lose or gain electrons easily. Therefore, the highest value of the oxidation number can vary depending on the transition element.

b) The first three groups:
The first three groups in the periodic table consist of alkali metals (Group 1), alkaline earth metals (Group 2), and boron group elements (Group 13). Alkali metals have an oxidation number of +1, alkaline earth metals have an oxidation number of +2, and boron group elements have an oxidation number of +3. Therefore, the highest value of the oxidation number in these groups is 1, 2, and 3, respectively.

c) In alkaline earth metals:
Alkaline earth metals belong to Group 2 of the periodic table, and their highest oxidation number is +2. Therefore, this option is not correct as it does not account for the highest value of 7.

d) Across the third period in the periodic table:
The third period in the periodic table consists of elements from sodium (Na) to chlorine (Cl). As we move across the period, the highest value of the oxidation number increases. Sodium (Na) has an oxidation number of +1, while chlorine (Cl) has an oxidation number of -1. The highest oxidation number in this period is +7, which is seen in the element manganese (Mn) when it forms the compound MnO4-. Therefore, option D is correct as it correctly identifies the highest value of the oxidation number across the third period.

Conclusion:
The highest value of the oxidation number changes from 1 to 7 across the third period in the periodic table. This is because the elements in the third period have different electronegativities and electron configurations, which affect their ability to gain or lose electrons and thus their oxidation states.