Magnitude of electron gain enthalpy of oxygen is less than that of fluorine but greater than that of — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Determine which subshells are being filled in the fifth period. These are the 5s, 4d, and 5p subshells. Step 2: Calculate the maximum number of electrons these subshells can collectively hold: 5s holds 2, 4d holds 10, and 5p holds 6. Step 3: The total number of electrons is 2 + 10 + 6 = 18. Since each element corresponds to the addition of one electron in the ground state configuration, there are exactly 18 elements in the fifth period.