Isoelectronic pair, among the following, is : 

1. ${\mathrm{ClO}}_2^{-}, {\mathrm{ClF}}_2^{+}$

2. ${\mathrm{IF}}_2^{-}, {\mathrm{I}}_3^{-}$

3. ${\mathrm{Cl}}_2\mathrm{O}, {\mathrm{ICl}}_2^{-}$

4. ${\mathrm{ICl}}_2^{-}, {\mathrm{ClO}}_2$

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 

Element of the third period that is expected to exhibit positive electron gain enthalpy is: 

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: