When the first ionization enthalpies ( _ i H ) of the second period elements (Li to Ne) are plotted against their atomic numbers ( Z ), the resulting curve exhibits a general upward trend but contains two specific anomalies where the ionization enthalpy drops compared to the preceding element. Let P represent the element at the first local maximum (peak) and Q represent the element at the local minimum (dip) immediat

Step-by-step solution

In the second period, the first ionization enthalpy generally increases from Li to Ne due to an increase in effective nuclear charge. However, there are two exceptions (anomalies) that appear as peaks followed by dips on the graph: 1. Beryllium (Be, 2s² ) has a higher ionization enthalpy than Boron (B, 2s² 2p¹ ) because it is more difficult to remove an electron from a fully filled, more penetrating 2s orbital than from a 2p orbital. Thus, the first peak P is Be, and the subsequent dip Q is B. 2. Nitrogen (N, 2s² 2