Consider the isoelectronic species, $\mathrm{Na}^{+}, \mathrm{Mg}^{2+}, \mathrm{F}^{-}$and $0^{2-}$. The correct order of increasing length of their radii is

Which of the following is not an actinoid?

The order of screening effect of electrons of $s, p, d$ and $f$ orbitals of a given shell of an atom on its outer shell electrons is

The first ionisation enthalpies of $\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}$ and Si are in the order

The electronic configuration of gadolinium (Atomic number 64) is

The statement that is not correct for periodic classification of elements is

Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is

The period number in the long form of the periodic table is equal to

The elements in which electrons are progressively filled in $4 f$-orbital are called

Which of the following is the correct order of size of the given species

The formation of oxide ion $0^{2-}(\mathrm{g})$, from oxygen atom requires first an exothermic and then an endothermic step as shown below

$$\begin{aligned} & \mathrm{O}(g)+e^{-} \rightarrow \mathrm{O}^{-}(g) ; \Delta H^{\mathrm{s}}=-141 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \mathrm{O}^{-}(g)+e^{-} \rightarrow \mathrm{O}^2(g) ; \Delta H^{\mathrm{s}}=+780 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}$$

Thus, process of formation of $\mathrm{O}^{2-}$ in gas phase is unfavourable even though $\mathrm{O}^{2-}$ is isoelectronic with neon. It is due to the fact that

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods (1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(i) The element with atomic number 57 belongs to

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods (1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(ii) The last element of the p-block in 6th period is represented by the outermost electronic configuration.

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods ( 1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(iii) Which of the elements whose atomic numbers are given below, cannot be accommodated in the present set up of the long form of the periodic table?

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods ( 1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(iv) The electronic configuration of the element which is just above the element with atomic number 43 in the same group is .............. .

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods ( 1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(v) The elements with atomic numbers 35,53 and 85 are all ............ .

Electronic configuration of four elements $A, B, C$, and $D$ are given below

A. $1 s^2 2 s^2 2 p^6$

B. $1 s^2 2 s^2 2 p^4$

C. $1 s^2 2 s^2 2 p^6 3 s^1$

D. $1 s^2 2 s^2 2 p^5$

Which of the following is the correct order of increasing tendency to gain electron?

Choose the correct order of atomic radii of fluorine and neon (in pm) out of the options given below and justify your answer.

Assertion (A) Generally, ionisation enthalpy increases from left to right in a period.

Reason (R) When successive electrons are added to the orbitals in the same principal quantum level, the shielding effect of inner core of electrons does not increase very much to compensate for the increased attraction of the electron to the nucleus.

Assertion (A) Boron has a smaller first ionisation enthalpy than beryllium.

Reason (R) The penetration of $2 s$ electron to the nucleus is more than the $2 p$ electron hence $2 p$ electron is more shielded by the inner core of electrons than the $2 s$ electrons.

Assertion (A) Electron gain enthalpy becomes less negative as we go down a group.

Reason (R) Size of the atom increases on going down the group and the added electron would be farther from the nucleus.

Which of the following elements can show covalencey greater than 4 ?

Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionisation (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame ?

Which of the following sequences contain atomic numbers of only representative elements?

Which of the following elements will gain one electron more readily in comparison to other elements of their group?

Which of the following statements are correct?

Which of the following sets contain only isoelectronic ions?

In which of the following options order of arrangement does not agree with the variation of property indicated against it?

Which of the following have no unit?

Ionic radii vary in

An element belongs to 3rd period and group 13 of the periodic table. Which of the following properties will be shown by the element?

Explain why the electron gain enthalpy of fluorine is less negative than that of chlorine?

All transition elements are $d$ - block elements, but all $d$ - block elements are not transition elements. Explain.

Identify the group and valency of the element having atomic number 119. Also predict the outermost electronic configuration and write the general formula of its oxide.

Ionisation enthalpies of elements of second period are given below Ionisation enthalpy/ $\mathrm{~k} \mathrm{~cal} \mathrm{~mol}^{-1}$ : 520, 899, 801, 1086, 1402, 1314, 1681, 2080. Match the correct enthalpy with the elements and complete the graph given in figure. Also write symbols of elements with their atomic number.

Among the elements $\mathrm{B}, \mathrm{Al}, \mathrm{C}$ and Si ,

(a) which element has the highest first ionisation enthalpy?

(b) which element has the most metallic character?

Justify your answer in each case.

Write four characteristic properties of $p$-block elements.

Illustrate by taking examples of transition elements and non-transition elements that oxidation states of elements are largely based on electronic configuration.

Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen. Explain.

First member of each group of representative elements (i.e., $s$ and $p$-block elements) shows anomalous behaviour. Illustrate with two examples.

p-block elements form acidic, basic and amphoteric oxides. Explain each property by giving two examples and also write the reactions of these oxides with water.

How would you explain the fact that the first ionisation enthalpy of sodium is lower than that of magnesium but its second ionisation enthalpy is higher than that of magnesium?

What do you understand by exothermic reaction and endothermic reaction? Give one example of each type.

Arrange the elements $\mathrm{N}, \mathrm{P}, 0$ and S in the order of

(i) increasing first ionisation enthalpy.

(ii) increasing non-metallic character.

Give reason for the arrangement assigned.

Explain the deviation in ionisation enthalpy of some elements from the general trend by using given figure.

Explain the following

(a) Electronegativity of elements increase on moving from left to right in the periodic table.

(b) Ionisation enthalpy decrease in a group from top to bottom.

How does the metallic and non-metallic character vary on moving from left to right in a period?

The radius of $\mathrm{Na}^{+}$cation is less than that of Na atom. Give reason.

Among alkali metals which element do you expect to be least electronegative and why?

Match the correct atomic radius with the element.

Match the correct ionisation enthalpies and electron gain enthalpies of the following elements.

Electronic configuration of some elements is given in Column I and their electron gain enthalpies are given in Column II. Match the electronic configuration with electron gain enthalpy.

Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.

Define ionisation enthalpy. Discuss the factors affecting ionisation enthalpy of the elements and its trends in the periodic table.

Justify the given statement with suitable examples-"the properties of the elements are a periodic function of their atomic numbers".

Write down the outermost electronic configurations of alkali metals. How will you justify their placement in group 1 of the periodic table?

Write the drawbacks in Mendeleef's periodic table that led to its modification.

In what manner is the long from of periodic table better than Mendeleef's periodic table? Explain with examples.

Discuss and compare the trend in ionisation enthalpy of the elements of group 1 with those of group 17 elements.