Rare gases are stable because they

Step 1: Analyze the question The question asks why rare (noble) gases such as helium, neon, and argon are stable, meaning chemically unreactive.

Step 2: The concept Stability in chemistry comes from having a full outermost electron shell.

• Helium has 2 electrons, a full first shell (the duplet).
• Neon, argon, krypton, and the others have 8 electrons in their outermost shell (the octet).

Because their outer shells are already full, these atoms have no tendency to gain, lose, or share electrons. That is why they are generally inert.

Step 3: Check each option

• A. Are chemically active: Wrong. Rare gases are chemically inert, which is the opposite of this.
• B. Equal number of protons and neutrons: Wrong. Many atoms have this, and it has nothing to do with stability. Argon-40 has 18 protons and 22 neutrons, for example.
• C. More electrons than protons: Wrong. Atoms are electrically neutral, so electrons equal protons. Having more electrons would make an ion.
• D. Have octet structures: Correct. A full outer shell (8 electrons, or 2 for helium) gives a stable electron configuration.

Step 4: Answer The correct option is D.

Tip: Remember "Full shell = Fully stable". When a WASSCE question asks why noble gases are unreactive, look for the options that mention an octet, a duplet, or a complete outer shell. Also, be careful with "chemically active", because it is a trap option that says the opposite of the truth.