Which of the following is true for valence electrons?
a) valence electrons are always located in the innermost energy level
b) each element in the periodic table has a different number of valence electrons.
c) valence electrons may be lost or gained by an atom when bonding occurs with another atom
d) when atoms collide with other atoms, they bond automatically

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.