Well, if you look at group 1 of the periodic table, you will notice a thrend. All elements in group 1 have 1 valence / outer electron. Then you look at period 2, 3, 4 and so on, you will see that the group number corresponds the number of valence/ outershell electrons. Hence, the group determines the electron(s) on the outershell.
I know what you're asking but I don't think the question is stated properly. Technically, an atom will not join with an "oxide" ion; i.e., the oxide ion is an atom of oxygen to which two electrons have been added. An oxide ion will add to 2 K ions or 1 Ca ion. The K ion has lost just one electron so it takes two of them to equal the 2- charge on the oxide ion whereas the Ca ion has lost two electrons and it takes only one of them to equal the charge on the oxide ion.
B. Hydrogen is the answer
This is the definition of a DNA mutation.
Depending on which part of the genome is affected, the consequences of a mutation may vary. A mutation is said to be hereditary if the mutated genetic sequence is transmitted to the next generation (see germinal mutations). It is one of the elements of biodiversity and one of the many factors that may be involved in the evolution of the species.
