JEE Main 2019 Chemistry question on Atomic Structure

In multielectron atoms, the energy of an orbital depends on the effective nuclear charge (Z_eff) experienced by the electron. The 2s orbital energy becomes more negative (lower) as Z_eff increases. Among H, Li, Na, and K, potassium has the highest nuclear charge (Z = 19), so despite shielding by inner electrons, the 2s electrons in K experience the greatest effective nuclear charge compared to Li (Z=3) and Na (Z=11). Greater Z_eff pulls the 2s orbital to a much lower (more negative) energy. Therefore, the 2s orbital energy is lowest (most stabilized) in K.