Which is most likely to be part of an ionic bond
a. an atom with no valence electron
b. an atom with one valence electron
c. an atom with two valence electrons
d. an atom with three valence electrons.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.