Excessive heating and repeated use of cooking oil is undesirable for several reasons. Firstly, option 1 states that the oil vapours produced can cause indoor pollution. This is true as the vapours can release harmful substances into the air and affect the quality of indoor air. Option 2 is correct in stating that carcinogenic substances like benzpyrene can be produced when cooking oil is heated excessively or used repeatedly. These substances are known to increase the risk of cancer. Option 3 suggests that the nutrient value of food may be lost. While this is possible to some extent due to high heat, it is not the main reason why excessive heating and repeated use of cooking oil is undesirable. Option 4 mentions the loss and wastage of oil, but this is not the primary concern, as the health risks associated with carcinogenic substances are the main issue.