Potassium chlorate (KClO\(_3\)) itself is not explosive under normal laboratory heating conditions (especially when mixed with a catalyst, which lowers the decomposition temperature). However, it is a very strong oxidizing agent. If the potassium chlorate comes into contact with easily oxidizable substances (carbonaceous materials like dust, rubber tubing, or grease) during the preparation, the mixture can become highly sensitive and explosive. This high risk of forming an explosive mixture is the primary reason why this method is usually not recommended in modern laboratories, favoring safer alternatives like the decomposition of hydrogen peroxide (H\(_2\)O\(_2\)).

The correct option is A - it forms explosive mixture with carbonaceous materials.