Answer:
Synthesis Reaction
General Formulas and Concepts:
Synthesis Reactions: A + B → AB
Decomposition Reactions: AB → A + B
Single-Replacement Reactions: A + BC → AB + C
Double-Replacement Reactions: AB + CD → AD + BC
Explanation:
Step 1: RxN
3C (s) + 4H₂ (g) → C₃H₈ (s)