Which metal is derived from the use of arsenate in pesticides?

Lead is the correct answer in this context because lead arsenate was historically used as a pesticide. In agricultural practices, arsenate compounds, particularly lead arsenate, were common in the early to mid-20th century for controlling pests in fruit crops. This pesticide became less favored due to concerns about its toxicity and the environmental impacts associated with lead.

Mercury, copper, and nickel do not directly derive from arsenate use in the same way lead does. Mercury has its own separate usage, often in relation to fungicides or as a contaminant but not linked specifically as a pesticide derived from arsenate. Copper compounds can also serve as fungicides or algaecides, while nickel is not primarily associated with pesticide applications at all. Thus, lead distinguishes itself through its historical application and the specific connection to arsenate in pesticide formulations.