Answer:
Double replacement.
Step-by-step explanation:
In the given reaction, there is not synthesis of compound.
The decomposition reactions are those in which a compound dissociates into simpler molecules or ions.
So the given reaction is not decomposition even.
In single replacement reactions, there is replacement of one group from a compound to other compound or element or ion.
Here two groups are being replaced (sulfate and nitrate) so the given reaction will be classified as double replacement.