The first financial model to use a Markov chain was from Prasad et al. in 1974. Another was the regime-switching model of James D. Hamilton (1989), in which a Markov chain is used to model switches between periods of high volatility and low volatility of asset returns.
A molecule is a particle containing two or more atoms. If it contains only one type of atom it is called an element.
The second one is a balanced chemical equation. C6H12O6 ...means one molecule of glucose, but we are much too lazy to put a figure 1 in front of the glucose molecule. The C6 .means that the glucose molecule contains 6 atoms of Carbon. The H12 .means that the glucose molecule contains 12 atoms of Hydrogen.