What is the scientific reason to the larger population of females than males in countries in relation to chromosomes?
There are several recessive disorders carried on the X chromosome (X-linked genes). Women may have a dominant normal gene on the other X chromosome to prevent the disorder from showing up in the phenotype. There would be no such dominant gene for males.
Although more males are born, partially because of these genetic disorders, women live longer.
http://en.wikipedia.org/wiki/Category:X-linked_recessive_disorders