To calculate how many grams NH3 will be formed from 6.0 g H2, the 2ND step you need
A) information about chemical reaction is
balanced or not.
B) set up given mole ratio of reactant vs.
products.
C) information about the mass of N2 reacting.
D) Set up mole ratios of reactants vs products
from balanced chemical equation.
N2 + H2 → NH3

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.