In which of the following series are the atoms arranged in order of increasing ionization energy?

Analyze the question: We need the series in which ionization energy goes up from left to right.

Concept:

• Going down a group, ionization energy decreases (the atoms get bigger and the outer electron is farther from the nucleus).
• Going across a period (left to right), ionization energy generally increases (nuclear charge rises and atomic radius shrinks).
• There are small exceptions across a period, such as Be > B and N > O.

Checking each option:

• A. Li, Na, K: These go down Group 1, so ionization energy decreases (Li > Na > K). This is decreasing, not increasing. ✗
• B. B, Be, Li: Ionization energies (kJ/mol) are B ≈ 801, Be ≈ 900, Li ≈ 520. The order B → Be → Li is 801 → 900 → 520, which is not increasing. ✗
• C. O, F, Ne: Ionization energies are O ≈ 1314, F ≈ 1681, Ne ≈ 2081. This is steadily increasing. ✓
• D. Be, Mg, Ca: These go down Group 2, so ionization energy decreases (900 → 738 → 590). ✗

Answer: Option C. O, F and Ne are in the same period (Period 2), and ionization energy rises from left to right as nuclear charge increases and atomic size decreases. Ne, a noble gas with a full outer shell, has the highest value.

Tip: For "increasing ionization energy" questions, look for elements in the same period arranged left to right. If the elements are in the same group, increasing ionization energy means going up the group. Always watch out for the Be/B and N/O exceptions.