Which statement describes a periodic trend of atomic radius?
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a. it tends to decrease from left to right across a period.
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b. it remains the same within a period.
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c. it remains the same within a group.
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d. it tends to decrease from top to bottom of a group.

A. It tends to decrease from left to right across a period

Explanation: This trend is caused by the increase number of protons in an atoms nucleus when moving across a period. The protons pull the electrons towards the nucleus causing the atomic radii to shrink and gets smaller or also called as electron shielding.

thats how its supposed to be