Which of the following is used to draw blood on an infant?

The correct answer is the 2.0 mm lancet, which is specifically designed for blood draws on infants, particularly for capillary blood sampling. Infants have smaller veins and their skin is thinner and more delicate compared to adults. A lancet, especially one with a designated depth like 2.0 mm, minimizes the risk of causing excessive pain and trauma while still allowing for sufficient blood collection from a fingertip or heel.

The other options are not typically suitable for drawing blood from infants. A standard needle and a butterfly needle, while useful for larger veins in older children and adults, could lead to complications such as excessive bleeding or difficulty accessing small veins. A Vacutainer system is also more appropriate for adult patients, as it typically involves using larger gauge needles and can be challenging to use safely on infants.