Question

In which of the following arrangements, the sequence is not strictly according to the property written against it?
(A) $C{{O}_{2}}$ < $Si{{O}_{2}}$ < $Sn{{O}_{2}}$ < $Pb{{O}_{2}}$; increasing oxidizing power
(B) HF < HCl < HBr < HI; increasing acid strength
(C) $N{{H}_{3}}$ < $P{{H}_{3}}$ < $As{{H}_{3}}$ < $Sb{{H}_{3}}$; increasing basic strength
(D) B < C < O < N; increasing first ionization enthalpy

Answer 1

The trend of the periodic table is specific for the groups and the periods. This trend depends upon the factors like nuclear force, atomic number, size etc. Ex: Atomic radius decreases from left to right in the period and increases down the group.

Complete step by step solution:
The general trend for the periodic table is responsible for the increasing and decreasing order of any specific quantity. Let us see them one by one,
Oxidizing power- The ability of the species to oxidize another species which results in reduction of itself. In short, oxidizing power is the ability to gain electrons. The oxidizing power of the elements of group XIV in the form of oxides; increases down the group as the ability to gain electrons increases. Thus, $C{{O}_{2}}$ < $Si{{O}_{2}}$ < $Sn{{O}_{2}}$ < $Pb{{O}_{2}}$ trend for increasing oxidizing power is correct.
Acidic strength- Acidic strength of an acid (having chemical formula as HX) is the tendency to dissociate into a ${{H}^{+}}$ ion and an anion as ${{X}^{-}}$.
The acidic strength of the elements of group XVII in the form of acids; increases down the group. As the atomic radius of a halogen increases, the bond formed by them becomes loose. Hence, dissociation becomes easy down the group resulting in a more acidic nature.
Thus, HF < HCl < HBr < HI trend for increasing acid strength is correct.
Basic strength-Basic strength is the ability of a species to accept ${{H}^{+}}$ ion from another species. The basic strength of the elements of group XV in the form of hydrides; decreases down the group. The presence of a lone pair of electrons on the group elements define its basic nature. As the size of the atom increases, the electron density decreases over the atom making it hard to donate those electrons. Thus, $N{{H}_{3}}$ < $P{{H}_{3}}$ < $As{{H}_{3}}$ < $Sb{{H}_{3}}$ trend for increasing basic strength is incorrect.
First ionisation enthalpy- The energy required to remove loosely held electrons to produce ions. This increases as we move from left to right in the period. The first ionisation enthalpy of the elements of period II increases as we move from left to right. However, there is an exception i.e. the first ionisation enthalpy of nitrogen is greater than that of oxygen. As nitrogen in a stable half-filled state is more stable than oxygen.
Thus, B < C < O < N trend for increasing first ionization enthalpy is correct.

Therefore, option (C) $N{{H}_{3}}$ < $P{{H}_{3}}$ < $As{{H}_{3}}$ < $Sb{{H}_{3}}$ ; increasing basic strength, is correct.

Note: Do note that the trend is continuous for any group or period but at times there can be exceptions with respect to the properties they are compared within.
So, do not blindly accept the option which would be showing some disengagement in the elements. Ex. In option (D).