It is easier to determine the electron configurations for the p-block elements in periods 1, 2, and 3 than to determine the electron configurations for the rest of the p-block elements in the periodic table because

In periods 1, 2, and 3, the p-block elements have electrons only in s and p orbitals; there are no intervening d orbitals to account for. In later periods, electron configurations also involve filled d subshells among the core electrons, making them more complex. Therefore, the correct choice is “their electrons are assigned to s and p orbitals only.”

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