Marking nut is

Ans. is 'a' i.e., Semicarpus anacardium Semicarpus anacardium (marking nut or bhilawan)* Its seed are heart shaped, conical and black with acrid oily juice which is brownish but turns black on exposure to air. Active principles are semecarpol and bhilawanol.* Juice applied to skin produces irritation, painful blisters followed by itching and eczema. Therefore it is used to produce artificial bruises.* It is also used by washerman to mark clothes.