Question 4
Name one thing that must be kept the same in both tubes in activity 17.2.
The right answer is the one marked above.
Putting the same number of equal, well-cleaned iron nails into both tubes. If the nails differed, their surface areas would differ too, and we could not say whether the result was caused by temperature or by surface area.
"Well-cleaned" matters as well — the surface of a rusty nail is rust, not iron.