D-block contraction refers to a phenomenon observed in the periodic table, particularly in the transition metals, where the d-orbitals are involved in bonding and chemical behavior. More specifically, it often describes the decrease in the size of the atoms of transition metals as you move from left to right across a period, despite an increase in the number of protons in the nucleus. This contraction is primarily due to the poor shielding effect of the d-electrons.
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