An element with the electron configuration of 1s 22s 22p 6 would have a combining power of

Analyze the question: The configuration 1s² 2s² 2p⁶ has 2 + 2 + 6 = 10 electrons, so the element is neon (atomic number 10). The question asks for its combining power, which is its valency.

Concept: Valency (combining power) is the number of electrons an atom gains, loses, or shares to reach a stable configuration. It depends on the outer shell.

Solution:

1. Count the electrons: 2 + 2 + 6 = 10, so the element is neon.
2. Look at the outer shell. The second shell (n = 2) holds 2s² 2p⁶ = 8 electrons. This is a complete octet.
3. A complete outer shell is already stable, so the atom has no need to gain, lose, or share electrons.
4. Neon therefore does not combine with other elements, and its combining power (valency) is zero.

The option "o" in A is a typo for 0. Options C and D are tempting because 8 is the number of outer electrons, but valency is not the same as the number of outer electrons. For elements with 4 or fewer outer electrons, valency equals that number. For elements with more than 4, valency is 8 minus the number of outer electrons. For 8 outer electrons, 8 − 8 = 0.

Answer: A (valency = 0).

Tip: All noble gases (He, Ne, Ar, Kr, Xe, Rn) have full outer shells, so their valency is 0. If you see a configuration ending in a full shell, such as 2p⁶ or 3p⁶, think "noble gas, so valency 0."