What subshell have lowest effective nuclear charge?

The subshell with the lowest effective nuclear charge is typically the 1s subshell. This is because electrons in the 1s subshell are closest to the nucleus and experience a significant amount of shielding from other electrons, which can result in a lower effective nuclear charge for outer subshells. However, when considering only the 1s electrons, they experience the full nuclear charge but are also influenced by electron-electron repulsions, making the effective nuclear charge feel lower for electrons in higher subshells.