Q.Match the correct atomic radius with the element.
Element | Atomic radius (pm)
Be | 74
C | 88
O | 111
B | 77
N | 66

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

Reasoning:

1. All five elements belong to Period 2. The order across the period is: Be, B, C, N, O.
2. Atomic radius decreases from left to right. So the largest radius should be for Be, and the smallest for O. …

The key concept here is periodic trend in atomic radius across a period. In the second period, as we move from left to right (Li → Be → B → C → N → O → F → Ne), the nuclear charge (number of protons) increases steadily. This stronger positive charge pulls the electron cloud inward, making the atom smaller. So the largest atom is on the far left, and the smallest is on the far right.

The given elements — Be, B, C, N, O — are all in the second period, in that exact order. So the atomic radii must decrease in the same sequence: Be (largest) > B > C > N > O (smallest).

Now look at the provided radii: 111, 88, 77, 74, 66. The largest is 111, the next is 88, then 77, then 74, and the smallest is 66. So we simply assign them in order.

1. Be is the leftmost element in this set, so it gets the largest radius: 111 pm.
2. B comes next, so it gets the next largest: 88 pm.
3. C follows B, so it gets 77 pm.
4. N follows C, so it gets 74 pm. …