Answer:
a. magnesium
b. nitrogen
Explanation:
Barium and magnesium are both in 2nd group, so most similar compounds.
Nitrogen - 15 group, so it forms least similar to barium compound.
Because both reactants and products continue to form. Option (c) is the answer.
I believe that the ice cube, being that it still has almost all of its properties, would still have a mass of 25 g after melting