The stability of + 1 oxidation state increases in the sequence:

Tl < In
In < Tl < Ga < Al
Ga < In < Al < Tl
Al

Solution

The stability of +1 oxidation state increases from aluminium to thallium i.e.Al < Ga < In < Tl.

The increasing order of the ionic radii of the given isoelectronic species is :

Cl^-, Ca²⁺, K⁺, S^2-
S^2-, Cl^-, Ca²⁺, K⁺
Ca²⁺, K⁺, Cl^-, S^2-
K⁺, S^2-, Ca²⁺, Cl^-

Which is the correct order of ionic sizes (At. No. : Ce = 58,Sn = 50, Yb = 70 and Lu = 71) ?

Ce >Sn > Yb >Lu
Sn > Ce > Yb >Lu
Lu >Yb > Sn > Ce
Sn > Yb > Ce >Lu

Solution

Correct order of ionic size is Sn > Ce > Yb > Lu.

Which of the following represents the correct order of increasing electron gain enthalpy with negative sign for the elements O, S, F and Cl ?

Cl < F < O< S
O< S < F < Cl
F< S < O < Cl
S< O< CI < F

Solution

O < S –1

Which of the following represents the correct order of ncreasing first ionization enthalpy for Ca, Ba, S, Se and Ar ?

Ca < S< Ba < Se
S < Se < Ca < Ba < Ar
Ba
Ca < Ba < S< Se

Solution

On moving along a period from left to right I.E. increase and on moving down a group I.E. decreases.hence correct order is : Ba < Ca < Se < S < Ar.

The correct order of electron gain enthalpy with negative sign of F, Cl, Br and I,having atomic number 9, 17, 35 and 53 respectively, is :

F> Cl >Br > I
Cl >F >Br > I
Br > Cl > I > F
I> Br > Cl > F

Solution

As we move down in a group electronga in enthalpy becomes less negative because the size of the atom increases and the distance of added electron from the nucleus increases. Negative electron gain enthalpy of F is less than Cl. This is due to the fact that when an electron is added to F, the added electron goes to the smaller n= 2 energy level and experiences significant repulsion from the other electrons present in this level.In Cl, the electron goes to the larger n = 3 energy level and consequently occupies a larger region of space leading to much less electron–electron repulsion. So the correct order is Cl > F >Br > I.

The correct sequence which shows decreasing order of the ionic radii of the elements is

Al³⁺ > Mg²⁺ > Na⁺ > F^- > O^2-
Na⁺ > Mg²⁺ > Al³⁺ > O^2- > F^-
Na⁺ > F^- > Mg²⁺ > O^2- > Al³⁺
O^2- > F^- > Na⁺ > Mg²⁺ > Al³⁺

Solution

All the given species contains 10 e–each i.e.isoelectronic.
For isoelectronic species anion having high negative charge is largest in size and the cation having high positive charge is smallest.

In which of the following arrangements, the sequence is not strictly according to the property written against it?

HF
NH₃ < PH₃ < AsH₃ < SbH₃ : increasing basic strength
B < C < O < N: increasing first ionization enthalpy
CO₂ < SiO₂ < SnO₂ < PbO₂ : increasing oxidising power

Solution

In hydrides of 15th group elements, basic character decreases on descending the group i.e.NH₃ > PH₃ > AsH₃ > SbH₃

Following statements regarding the periodic trends of chemical reactivity of the alkali metals and the halogens are given. Which of these statements gives the correct picture?

Chemical reactivity increases with increase in atomic number down the group in both the alkali metals and halogens
In alkali metals the reactivity increases but in the halogens it decreases with increase in atomic number down the group
The reactivity decreases in the alkali metals but increases in the halogens with increase in atomic number down the group
In both the alkali metals and the halogens the chemical reactivity decreases with increase in atomic number down the group

Solution

The alkali metals are highly reactive because their first ionisation potential is very low and hence they have great tendency to loses electron to form unipositive ion.
On moving down group- I from Li to Cs ionisation enthalpy decreases hence the reactivity increases. The halogens are most reactive elements due to their low bond dissociation energy, high electron affinity and high enthalpy of hydration of halide ion. However their reactivity decreases with increase in atomic number

What is the value of electron gain enthalpy of Na⁺ if IE₁ of Na = 5.1 eV ?

–5.1 eV
–10.2 eV
+2.55 eV
+10.2 eV

Solution

IE₁ of Na = –Electron gain enthalpy of Na⁺ = – 5.1 eV

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