The correct option is A Vulcanization
Vulcanisation of Rubber - Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperature (<283 K) and shows high water absorption capacity.
The process of vulcanisation includes heating of raw rubber with sulphur and an appropriate additive at temperature range between 373 K to 415 K. Sulphur foms crosslinks at reactive sites of double bonds and thus, rubber gets stiffened.