The ion formed by chlorine gas when it reacts with sodium metal hasA. 17 protons and 18 electrons.B. 17 protons and 17 electrons.C. 17 protons and 16 electrons.D. 16 protons and 17 electrons.

To determine the correct answer, let's analyze the reaction between chlorine gas (Cl₂) and sodium metal (Na).

1. Identify the elements involved:

   • Chlorine (Cl)
   • Sodium (Na)

2. Understand the nature of the reaction:

   • Sodium (Na) is a metal and tends to lose one electron to form a cation (Na⁺).
   • Chlorine (Cl₂) is a non-metal and tends to gain one electron to form an anion (Cl⁻).

3. Determine the ion formed by chlorine:

   • Chlorine gas (Cl₂) consists of two chlorine atoms. Each chlorine atom will gain one electron.
   • When a chlorine atom gains one electron, it forms a chloride ion (Cl⁻).

4. Calculate the number of protons and electrons in the chloride ion (Cl⁻):

   • The atomic number of chlorine (Cl) is 17, which means it has 17 protons.
   • In its neutral state, chlorine also has 17 electrons.
   • When chlorine gains one electron to form Cl⁻, it will have 18 electrons.

5. Summarize the findings:

   • The chloride ion (Cl⁻) formed by chlorine gas when it reacts with sodium metal has 17 protons and 18 electrons.

Therefore, the correct answer is: A. 17 protons and 18 electrons.