Question

Which of the following statements is correct in regards to assigning oxidation numbers?

1) Alkali metals can have an oxidation number of either +1 or -1
2) Halogens can never have an oxidation number of -1
3) Oxygen must always have an oxidation number of -2, even in its elemental form
4) The oxidation number of alkaline earth metals in ionic compounds is always +2

Answer 1

The correct statement regarding oxidation numbers is that the oxidation number of alkaline earth metals in ionic compounds is always +2. This is true for elements in the second column of the periodic table, such as magnesium in MgCl2.

Step-by-step explanation:

Correct Statement Regarding Oxidation Numbers

When considering the correct statement about assigning oxidation numbers, we must look at the rules and common oxidation states of elements. For the options given:

1. Alkali metals in the first group/column of the periodic table usually have an oxidation number of +1, not -1.
2. Halogens, particularly fluorine, have an oxidation number of -1 when in most compounds, unless they are combined with oxygen or other halogens, where they can have positive oxidation numbers.
3. Oxygen in most compounds has an oxidation number of -2, but this can vary, such as in peroxides (O₂²-) where it is -1, or in compounds with fluorine where it can have positive values.
4. The oxidation number of alkaline earth metals in ionic compounds is indeed always +2, making this the correct statement among the options provided.

Examples:

For instance, in MgCl2, magnesium, an alkaline earth metal, has an oxidation number of +2 while each chlorine atom has an oxidation number of -1. In its elemental form, magnesium would have an oxidation number of 0.