The correct answer is option 1: Crude oil prices. The Brent index is a widely used benchmark for the pricing of crude oil. It represents the average prices of different types of crude oil extracted from the North Sea. This index is named after the Brent oilfield, which is one of the primary sources of the crude oil used for pricing.

Option 2, Copper future prices, is not relevant to the Brent index. Copper futures prices are associated with the trading of copper as a commodity, not crude oil.

Option 3, Eco-friendly status of processed foods, is also not relevant to the Brent index. The Brent index is focused on pricing crude oil and does not have any connection with processed foods.

Option 4, Energy efficiency status of electrical goods, is also unrelated to the Brent index. Energy efficiency status pertains to the energy consumption of electrical goods, while the Brent index solely focuses on crude oil prices.

In summary, the Brent index is specifically associated with option 1: Crude oil prices.