Question

which does a shotgun shell have that a cartridge does not?
wad
primer
casing
projectiles
question 16
which can associate a suspect and the firing of a gun?
powder residues
markings on the guns exterior
markings on the bullet
markings on the casing

Explanation:

For the first question, a shotgun shell contains a wad which separates the shot from the powder and helps with shot - pattern control, and cartridges typically do not have wads. For the second question, powder residues can be transferred to a suspect's hands or clothing when they fire a gun, associating them with the firing event.

Answer:

First question: wad
Second question: powder residues