What percentage of bonds have the most common combination of atoms' elements?
DIVIDE(COUNT(bond_id), COUNT(atom_id where MAX(COUNT(atom_id)) ))
SELECT CAST((SELECT COUNT(T1.atom_id) FROM connected AS T1 INNER JOIN bond AS T2 ON T1.bond_id = T2.bond_id GROUP BY T2.bond_type ORDER BY COUNT(T2.bond_id) DESC LIMIT 1 ) AS REAL) * 100 / ( SELECT COUNT(atom_id) FROM connected )