Which compound can decolourise acidified potassium manganate(VII) solution?
Na2SO4\text{Na}_2\text{SO}_4Na2SO4
K2CO3\text{K}_2\text{CO}_3K2CO3
Na2SO3\text{Na}_2\text{SO}_3Na2SO3
KNO3\text{KNO}_3KNO3