Aqueous solution is alkaline in case of 

1) Na₂CO₃ is salt of WA(H₂CO₃) and SB(NaOH) hence its solution is alkaline
2) CuSO₄ is salt of SA(H₂SO₄) and WB(Cu(OH)₂) hence the solution is acidic
3) NH₄Cl is salt of SA(HCl) and WB(NH₄OH) hence the solution is acidic
4) K₂SO₄ is salt of SA (H₂SO₄) and SB(KOH) hence the solution is neutral