Which row correctly names the gas?
- A$\text{Cl}_2$; damp litmus paper; the litmus paper turns blue
- B$\text{NH}_3$; damp litmus paper; the litmus paper turns red
- C$\text{O}_2$; limewater; no change is observed
- D$\text{SO}_2$; acidified aqueous potassium manganate(VII); the colour of the solution changes from purple to colourless