Concept:
Whitewares are ceramic products made from white burning clays and other raw materials. Their firing temperatures depend on their degree of vitrification.
Step 1: Earthenware and terracotta are usually fired at comparatively lower temperatures.
Step 2: Stoneware is fired at a higher temperature than earthenware, but it is generally lower than porcelain.
Step 3: Porcelain is a highly vitrified whiteware product.
Step 4: It requires high temperature firing to develop:
• high strength,
• translucency,
• low water absorption,
• dense body.
Step 5: Hence, among the given whitewares, porcelain has the highest firing temperature.
Therefore, the correct answer is:
\[
\boxed{\text{Porcelain}}
\]