161.
The correct order of decreasing electronegativity values among the elements (i) - beryllium, (ii) - oxygen, (iii) - nitrogen and (iv) - magnesium is
Electronegativity values of given elements are as follows :
$$\eqalign{
& Be - 1.5\left( {\text{i}} \right)\,\,\,\,\,\,\,\,\,\,\,\,Mg - 1.2\left( {{\text{iv}}} \right) \cr
& O - 3.5\left( {{\text{ii}}} \right)\,\,\,\,\,\,\,\,\,\,\,\,N - 3.0\left( {{\text{iii}}} \right) \cr
& {\text{i}}{\text{.e}}{\text{.}}\,\,\left( {{\text{ii}}} \right){\text{ > }}\left( {{\text{iii}}} \right){\text{ > }}\left( {\text{i}} \right){\text{ > }}\left( {{\text{iv}}} \right) \cr} $$
162.
Which one of the following groups represents a collection of isoelectronic species? $$\left( {{\text{At}}{\text{.}}\,{\text{nos}}.:Cs - 55,Br - 35} \right)$$
Generally, the ionization enthalpies or energy increases from left to right in a period and decreases from top to bottom in a group. Several factor such as atomic radius, nuclear charge, shielding effect are responsible for change of ionization enthalpies.
Here, Ist ionization enthalpy of $$A$$ and $$B$$ is greater than group $$I\left( {Li = 520\,kJmo{l^{ - 1}}\,{\text{to}}\,Cs = 374\,kJ\,mo{l^{ - 1}}} \right),$$ which means element $$A$$ and $$B$$ belong to group –2 and all three given ionization enthalpy values are less for element $$B$$ means $$B$$ will come below $$A.$$
166.
Few values of enthalpies are given below :
$$\eqalign{
& O = - 141\,kJ\,mo{l^{ - 1}} \cr
& F = - 328\,kJ\,mo{l^{ - 1}} \cr
& S = - 200\,kJ\,mo{l^{ - 1}} \cr
& Cl = - 349\,kJ\,mo{l^{ - 1}} \cr} $$
What do these values show?
No explanation is given for this question. Let's discuss the answer together.
169.
The electronic configuration of few elements is given below. Mark the statement which is not correct about these elements.
$$\eqalign{
& \left( {\text{i}} \right)1{s^2}2{s^2}2{p^6}3{s^1} \cr
& \left( {{\text{ii}}} \right)1{s^2}2{s^2}2{p^5} \cr
& \left( {{\text{iii}}} \right)1{s^2}2{s^2}2{p^6} \cr
& \left( {{\text{iv}}} \right)1{s^2}2{s^2}2{p^3} \cr} $$