Answer:
2. Substance XYZ breaks down into X, Y, and Z.
Explanation:
In a <em>decomposition reaction</em>, one substance breaks down into two or more simpler substances. Thus, the reaction
XYZ ⟶ X + Y + Z
is a decomposition reaction.
1. is <em>wrong</em><em>.</em>
P + XY ⟶ PY + X
is a <em>displacement</em> reaction.
3. is <em>wrong</em>.
2Z + O₂ ⟶ 2ZO
is an <em>oxidation</em> or a<em> combination</em> <em>reaction</em>.
4 is <em>wrong</em>.
X + Y ⟶ XY
is a <em>combination reaction</em>.
