Answer

`A to c`
`B to d`
`C to b`
`D to a`

Explanation

A → c Lead nitrate is decomposed into PbO, `NO_2` and `O_2`
B → d Zinc displaces iron from `FeSO_4`
C → b Mutual exchange of ions takes place when NaCl and `AgNO_3` react
D → a Sulphur combines with oxygen to form sulphur dioxide