Which one of the following is an isoelectronic pair?

1. ${\mathrm{ClO}}_2^{-},<mspace\; width="1em"></mspace>{\mathrm{ClF}}_2^{+}$

2. ${\mathrm{IF}}_2^{-},<mspace\; width="1em"></mspace>{\mathrm{I}}_3^{-}$

3. ${\mathrm{Cl}}_2\mathrm{O},<mspace\; width="1em"></mspace>{\mathrm{ICl}}_2^{-}$

4. ${\mathrm{ICl}}_2^{-},<mspace\; width="1em"></mspace>{\mathrm{ClO}}_2$

The most non-metallic element among the given elements is

The pair that has both members from the same period of the Periodic Table is 

Which of the following third-period elements has a positive electron gain enthalpy?

The total number of 3rd period elements with more than one electron in a 3d orbital is:

The group of metals having the positive value of electron gain enthalpy is:

Percentage ionic character, if electronegativity value of X=2.1 & Y=3.0, is :-

The correctly matched option is:-

1. ${\mathrm{Fe}}^{+3}>{\mathrm{Fe}}^{+2}$ $>$ ${\mathrm{Fe}}^{+}$  : Order of atomic radius 

2. O > C > B > N   : Order of ionisation energy 

3. ${\mathrm{O}}^{-2}$ $<{\mathrm{O}}^{-}$ $<\mathrm{O}$ $<{\mathrm{O}}^{+}$ :  Increasing order of Z_eff

4. O < N < F < Ne  :  Order of electron affinity

The incorrect order of electronegativity is :

For the second-period elements, the correct increasing order of first ionisation enthalpy is: