Which of the following pairs of application and principle is INCORRECT?

1. ACottrell precipitator removes smoke because charged smoke particles are discharged at oppositely charged electrodes
2. BStyptic pencil ($\mathrm{FeCl}{}_3$) stops bleeding because $\mathrm{Fe}{}^{3+}$ peptizes the blood sol
3. CDelta formation occurs because electrolytes of sea water coagulate the negatively charged clay sol
4. DAlum purifies turbid water because $\mathrm{Al}{}^{3+}$ coagulates negatively charged suspended impurities