HELPPP WILL MARK BRAINIEST 18. An incident light beam strikes the edge of its medium at an angle of 42°. The beam refracts at an angle of
90?. Now you know that
a. The critical angle of the medium is 42?.
b. If you decrease the incident angle, the refracted beam will exit the medium.
c. If you increase the incident angle, the refracted beam will not exit the medium
d all of the above

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -

The rearrangement of particles in a physical change. hope this