Matt's cube, after 5 trials, had an average density of 7.40 g/cm3 . his group's cube was made of
a) aluminum.
b) gold.
c) nickel.
d) zinc.

The right answer for the question that is being asked and shown above is that: "B) gold." Matt's cube, after 5 trials, had an average density of 7.40 g/cm3 . His group's cube was made of B) gold. 

Naoh + hbr -> nabr (salt) + h2o ca (oh)2 + 2hbr - - - > ca (br)2 + 2h2o

Well you can immediately rule out a and d because if a metal were to lose or gain protons, then it would become a different element all together. the answer here is b because the positive symbol with a number refers to how many electrons the metal can give away to become stable.