When determining whether a chemical reaction has taken place, you observe and look for several indicators. which would be considered an indication that a chemical reaction or chemical change has taken place?
a) solid melts.
b) heat is given off.
c) substance dissolves
d) substance changes shape.

The answer would be B, heat is given off. Steam, bubbling, and fizzing can also indicate that a chemical change is occurring.  

3is a crest4 is a trough 2 is the amplitude 1 is the wavelength

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 -