Dear Student,
Ans1. Mangoes are sundried before pickling in order to keep it for long term to dry all iys moisture content.
Ans 2. Addition of salt to pieces of mangoes so that the salt absorbs water from the pieces,because,water spoils pickle and prevents it from long usage as water enables growth of micro organisms and pickle is attacked by fungus if water is present. So salt is used in preservation.
sodium benzoate is the other preservative used.
Regards