Which of the following is correct regarding atomic radius?
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Atomic radius generally increases down a group due to additional electron shells, and decreases across a period due to increased effective nuclear charge pulling electrons closer.
Let's evaluate the options:
Fe ≈ Co ≈ Ni: These are period 4 transition metals. Their radii are very similar due to lanthanide contraction, so this is plausible.
NO ≈ F: Nitrogen and oxygen are smaller than fluorine. This is incorrect.
O ≈ S ≈ Se: Oxygen (period 2) is much smaller than sulfur (period 3) and selenium (period 4). This is incorrect.
B ≈ Al ≈ Ga: Boron (period 2) is smaller than aluminum (period 3). Gallium (period 4) is similar in size to aluminum due to poor shielding by d-electrons. This is incorrect.
Final Answer: Fe ≈ Co ≈ Ni