Which carcinogenic molecule have the highest number of atoms consisted in it?
label = '+' mean molecules are carcinogenic; molecule that have the highest number of atoms consisted in in refers to MAX(COUNT(atom.molecule_id))
SELECT T.molecule_id FROM ( SELECT T2.molecule_id, COUNT(T1.atom_id) FROM atom AS T1 INNER JOIN molecule AS T2 ON T1.molecule_id = T2.molecule_id WHERE T2.label = '+' GROUP BY T2.molecule_id ORDER BY COUNT(T1.atom_id) DESC LIMIT 1 ) t