16 neutrons are present in the most abundant isotope.
Explanation:
Phosphorus has 18 isotopes. The most common isotope has mass number (no. of protons 15+ no. of neutrons 16=) 31 .
Allele frequencies in a population may change due to four fundamental forces of evolution: Natural Selection, Genetic Drift, Mutations and Gene Flow. Mutations are the ultimate source of new alleles in a gene pool. Two of the most relevant mechanisms of evolutionary change are: Natural Selection and Genetic Drift.
I believe that classical conditioning is a type of learning in which a neutral stimulus comes to elicit a response after being paired with a stimulus that would elicit the same response naturally. It is where a conditioned stimulus becomes associated with an unrelated unconditioned stimulus in order to produce a behavioral response which is referred to as a conditioned response.