Final answer:
The oxidation number of alkali metals in a compound is always +1, making the statement true. This rule applies to all alkali metals due to their single valence electron which they lose in reactions, resulting in a +1 oxidation state.
Step-by-step explanation:
The oxidation number of alkali metals in a compound is indeed always +1. This statement is true (Option A). Alkali metals, which are the elements found in the first column of the periodic table, have a single valence electron that they readily lose in chemical reactions, resulting in an oxidation state of +1. For instance, the oxidation number for sodium (Na) is always +1 in its compounds. This rule holds regardless of the type of compound the alkali metal is a part of, whether it is an ionic compound like sodium chloride (NaCl) or a more complex compound. Conversely, alkaline earth metals, found in the second column of the periodic table, typically exhibit an oxidation state of +2 due to their two valence electrons. It is also important to note that the concept of an oxidation number refers to individual atoms within a compound and is not a cumulative measure for all atoms of that element in the compound.