Statement I: Amino acids are substituted methanes as there are four substituent groups occupying the four valency positions. 

Statement II: The four valency positions of carbon are substituted by hydrogen, carboxyl group, amino group and a variable group designated as R group. 

Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon i.e., the α-carbon. Hence, they are called α-amino acids. They are substituted methanes. There are four substituent groups occupying the four valency positions. These are hydrogen, carboxyl group, amino group and a variable group designated as R group.