Final answer:
Only option C (Zn + 2HCl → H₂ + ZnCl₂) is a correctly balanced chemical equation, as it has an equal number of each type of atom on both sides.
Step-by-step explanation:
The student has asked which of the following reactions is correctly balanced: A) N₂ + H → 2NH₃, B) 2H₂O + C → CO + 2H₂, C) Zn + 2HCl → H₂ + ZnCl₂, D) CO + O₂ → CO₂. To determine if a reaction is balanced, one must count the atoms of each element on both sides of the reaction. For example, reaction D (CO + O₂ → CO₂) is balanced because there is one carbon atom and two oxygen atoms on both sides of the equation. Let's apply this process to check each option.
Option A is incorrect because there is no coefficient before "H" to indicate how many hydrogen atoms are there, making the reaction unbalanced. Option B is incorrect because the carbon and oxygen atoms are not balanced (there should be two carbon atoms on the product side to match with C). In option C, the zinc and chlorine atoms as well as the hydrogen atoms are balanced, making this reaction correctly balanced. While option D is a frequently seen balanced combustion reaction, it was not listed among the options provided by the student.