A neon atom is chemically nonreactive because

Step 1: Analyze the question We are asked why neon is chemically unreactive (inert). This is about electronic structure and stability.

Step 2: The concept Atoms react by gaining, losing, or sharing electrons to achieve a stable, full outer shell (the octet rule, or duplet for helium). Noble gases (Group 18/0) already have this arrangement, so they have no tendency to react.

Step 3: Neon's electronic configuration

• Neon has atomic number 10.
• Electronic configuration: 2, 8 (1s² 2s² 2p⁶)
• Its outer shell (the second shell) holds a maximum of 8 electrons, and neon has exactly 8, so the shell is completely filled.

Step 4: Check each option

• A. Partially filled outer shell: wrong, it is full.
• B. Protons equal electrons: true of every neutral atom, so it does not explain neon's inertness.
• C. Outer electron shell is completely filled: correct. This gives neon a very stable configuration, high ionization energy, and almost no tendency to gain or share electrons.
• D. Equal protons and neutrons: neon-20 does have 10 and 10, but this is about the nucleus and has nothing to do with chemical reactivity.
• E. No electrons in the outer shell: wrong, it has 8.

Answer: C

Tip: Chemical reactivity depends on the outermost electrons. When you see "noble gas" or "inert" in a question, think "full outer shell" (octet, or duplet for helium).