A Markov chain is a discrete random process with the property that the next state depends only on the current state (wikipedia). A Markov chain is a discrete random process with the property that the next state depends only on the current state (wikipedia). So $P(X_n | X_1, X_2, \ldots X_n-1) = P(X_n | X_{n-1})$.
Some people find molecules and compounds confusing. Here's how to remember the difference. If you join two different chemical elements together, you can often make a completely new substance. Glue two atoms of hydrogen to an atom of oxygen and you'll make a single molecule of water.
A molecule, however, is composed of more than one atom. Some elements exist naturally as molecules. For example, hydrogen and oxygen exist as two-atom molecules. Other elements also exist naturally as diatomic moleculesA molecule with only two atoms. (see Table 3.3 Elements That Exist as Diatomic Molecules).As with any molecule, these elements are labeled with a molecular formulaA formal listing of what and how many atoms are in a molecule. molecule, however, is composed of more than one atom. Some elements exist naturally as molecules. For example, hydrogen and oxygen exist as two-atom molecules. Other elements also exist naturally as diatomic moleculesA molecule with only two atoms. (see Table 3.3 Elements That Exist as Diatomic Molecules).