Correlate the items listed in Column I with those listed in Column II. 

Column I Column II
A. Synthesis gas 1.  Na2[Na4(PO3)6 ]
B. Heavy water 2. Mixture of CO and H2
C. Calgon 3. Prolonged electrolysis of water
D.  Salt like hydrides 4. Stoichiometric compounds of s-block elements

Codes

A B C D
1. 4 3 2 1
2. 2 3 1 4
3. 1 4 3 2
4. 4 1 3 2