Starch-iodide paste/paper is used as an external indicator in one of the following titrations. Identify that.
1
Iodometric titration of copper sulphate using sodium thiosulphate as titrant
2
Iodimetric titration of ascorbic acid using iodine solution as titrant
3
Diazotization titration of sulphadiazine using sodium nitrite as titrant
4
Potassium dichromate titration using sodium thiosulphate as titrant