Chemistry S & P Block Elements MDCAT 2015
PMDC Verified Question 91 of 104
Keeping in view the size of atoms, which order is correct?
A
N > C
B
Ar > Cl
C
P > Si
D
Li > Be
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Li > Be
Concept:

Atomic size (radius) decreases across a period from left to right due to increasing effective nuclear charge. It increases down a group due to the addition of new electron shells.

Solution:

  • Lithium (Li, Atomic No. 3) and Beryllium (Be, Atomic No. 4) belong to the same period (Period 2).
  • Because Li is to the left of Be, Li experiences less effective nuclear charge.
  • Therefore, the atomic radius of Li is larger than that of Be (Li > Be).


Why other options are incorrect:

  • Option A: Nitrogen is to the right of Carbon, so N < C.
  • Option B: Argon is to the right of Chlorine, so Ar < Cl.
  • Option C: Phosphorus is to the right of Silicon, so P < Si.

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