Question

which of the following atoms is the smallest?
be
o
li
b
ne
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Explanation:

Step1: Recall periodic trend

Atomic radius decreases across a period (left to right) due to increasing nuclear charge, pulling electrons closer.

Step2: Identify period

Be, O, Li, B, Ne are in period 2. Order: Li (leftmost), Be, B, O, Ne (rightmost).

Step3: Apply trend

Across period 2, atomic radius decreases left to right. O is to the right of Li, Be, B. Ne is a noble gas with van der Waals radius (larger than covalent radius of O in bonding context, but for neutral atoms in same period, effective nuclear charge: O has \( Z_{eff} \) higher than B, Be, Li. So O is smaller than Li, Be, B. Ne's radius is larger as noble gas (uses van der Waals). So O is the smallest among these.

Answer:

O (the option with "O" is correct, which is the second option in the list: "O" with the blue selected circle)