Natural selection in a population leads to evolution when: a. every new generation of the population is a new species. b. an offspring does not have all the same traits as its parents. c. an organism cannot reproduce because of a mutation. d. allele frequencies of some traits change in the population.

D) allele frequencies of some traits change in the population

Alleles can be phenotype (how they appear) and natural selection is when an organism changes in a way that helps them survive.

It can be the way their beaks are formed that gives them a better chance of catching food among other stuff (Darwin's investigation)
Or how they change their color to adapt to the sudden change in tree coloration (Pepper moths)

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass