Which of the following is not a correct chemical equation for a double displacement reaction? (d? )

2hno3 + mg(oh)2 yields 2h2o + mg(no3)2

h3po4 + 3naf yields 3hf + na3po4

2kno2 + baso4 yields k2so4 + ba(no2)2

4nabr + co(so3)2 yields br2so3 + cona4

The correct answer would be the last option. A double displacement type of reaction involves the switching of places the cations and anions accordingly. The given reaction is erroneous since in the product side the anions and cations are being paired which would not make sense. The correct reaction should be 

4NaBr + Co(SO3)2 yields CoBr4 + 2Na2SO3

Tolerance to high levels of salinity