The craftspersons of Bidar were so famed for their inlay work in __________ .

Copper and Silver

The correct answer is Option (4) - Copper and Silver

Bidriware is known for its unique metal inlay work, where silver or other metals are inlaid onto a base of black metal, typically a zinc alloy. While gold can sometimes be a very rare and expensive element used in some Bidri pieces, the most common and characteristic combination is copper and silver.