Question

The atomic radii of two elements $X$ and $Y$ are $0.72\stackrel{\circ }{A}$ and $1.6\stackrel{\circ }{A}$ respectively. Then the elements $X$ and $Y$ are respectively:

• A. $F$ and $Ne$
• B. $Ne$ and $F$
• C. $Li$ and $Be$
• D. $Fe$ and $F{e}^{2+}$ ion

Answer 1

Answer: (A)

$F$ and $Ne$

The fluorine atom has 5 electrons in its 2p atomic orbital(one electron less than the ideal gas configuration). Hence nuclear charge and nuclear attraction force are higher comparatively which results in the decrease of the radius. So the element having 0.72$A^{\circ }$ atomic radii will be F.

Ne is a noble gas. For noble gases, van der Waals radii are generally considered which are quite high than the atomic radii. So the element having atomic radii 1.6 $A^{\circ }$ will be Ne.

Option A is correct.