Question

In which of the following arrangements, the order is NOT according to the property indicated against it?

• A. Li < Na < K < Rb : Increasing metallic radius
• B. KBr < F < Cl: Increasing electron gain enthalpy (with negative sign)
• C. B < C < N < O Increasing first ionization
• D. ​ < < < Increasing ionic size
  

Answer 1

The correct option is C

B < C < N < O Increasing first ionization

We Know,

Atomic radius increases down the group because of increase in principal quantum number.

Therefore, Li < Na < K < Rb.

And We know more the cationic charge, smaller the size of ion in isoelectronic species because the nuclear charge remains the samebut the number of electrons decreases.

Therefore, ${Al}^{3+}$ < ${Mg}^{2+}$ < ${Na}^{+}$ <$F^{-}$

Now, Electron gain enthalpy decreases down the group, but

Cl > F [Because of small size, higher density, greater electronic repulsion of Flourine]

Therefore, Br < F < Cl.

And, Ionization enthalphy $\alpha$ $\frac{1}{AtomicRadius}$

but for N and O

N > O

because of half filled p- orbitals which makes Nitrogen very stable and it is very tough to remove the electron.

Therefore,

B < C < O < N