Final answer:
Gunpowder residue is most likely to be found on the thumb web of a shooter's hand, an area vulnerable to particles ejected from a firearm during firing. This location is designated as the correct answer, considering the shooter's grip and proximity to the discharge points on common firearms. D is the correct answer.
Step-by-step explanation:
When a person fires a gun, gunpowder residue often deposits on the shooter's hands due to the explosive discharge of the firearm. The most common areas where one might find gunpowder residue include the thumb web, the index finger, and other parts of the hands that are near the firearm's grip and ejection port when it is fired.
However, the presence of residue can vary based on several factors such as the type of firearm, the manner in which it is held, and the actions of the shooter immediately after firing.
Among the options provided, the thumb web is the most likely place for gunpowder residue to appear. This is the area between the thumb and the index finger, which is typically the part of the hand closest to the cylinder gap (in revolvers) or the ejection port (in semiautomatic pistols) where hot gases and particles expel upon discharging the firearm. Additionally, during the act of firing, the shooter's grip often causes the hands to enclose this space, catching more particles. Therefore, the mentioned correct option in final answer is (d) the thumb web.