What are the classification of dangerous goods as per IMDG code ?

Class 6: Toxic and infectious substances

Class 6.1: toxic substances
Class 6.2: infectious substances

Class 7: Radioactive material

Class 8: Corrosive substances

Class 9: Miscellaneous dangerous substances and articles

The numerical order of the classes and divisions is not that of the degree of danger 

Class 10: Marine pollutants

Marine pollutants shall be classified in accordance with chapter 2.9.3 in IMDG Code.

Note :-

The IMDG code is a very much living document and gets amended from time to time (every 2 years). In the last decade major changes were made to Ems-emergency medical schedule, MFAG and INF codes (carriage of nuclear materials)
IMDG Code means the International Maritime Dangerous Goods (IMDG) Code adopted by the Maritime Safety Committee of the Organization by resolution MSC.122(75)
The objective of the IMDG Code is to enhance the safe carriage of dangerous goods while facilitating the free unrestricted movement of such goods and prevent pollution to the environment