NCERT Exemplar Class 12 Chemistry Chapter 7 Solutions: The p-Block Elements

NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements will help you to revise the complete CBSE syllabus. This chapter of NCERT Exemplar Class 12 Chemistry Solutions Chapter 7 covers all aspects of the chapter such as inorganic ring system of the P block element that has a long and respected history of chemistry dating back to the early 19th century. The elements of groups 13, 14, 15, 16, 17, 18 are called p block elements. They represent the typical external electronic configuration ns2np1-6. The P block elements are present in all three physical conditions and are probably metallic, non-metallic, or semi-metallic.

NCERT exemplar solution will also help you to understand Group 15 Elements (Dinitrogen, Ammonia, Oxides of Nitrogen), Group 16 Elements (Dioxygen, Simple Oxides, Ozone, Sulphur — Allotropic Forms ), Group 17 Elements (Chlorine, Hydrogen Chloride ). The experts in the field explain the solutions very clearly and include all the basic concepts/theories and rules of chemistry.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements has a total of 72 questions that are divided into 5 sections touching all the topics based on Chapter 7. The questions are of various kinds which will help you get a complete revision with the help of MCQ’S, short answer questions, fill in the blanks, true or false, numerical questions, worksheets and exercises to assist you in the preparation of CBSE Class 12 board and other entrance exams.

Important Topics for NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements

  • Elements of block p: Elements that belong to groups 13-18 of the periodic table.
  • General electronic configuration of p-block elements: The elements of the p-block are characterized by the electronic configuration of the ns2np1-6 valence layer.
  • Representative elements: The elements that belong to the s and p blocks in the periodic table.
  • The effect of an inert pair: The tendency of the ns2 pair to participate in a bond formation decreases with increasing atom size. This trend is called the “inert pair effect.” In other words, the energy required for electron division is greater than the energy released during the formation of two additional bonds.
  • Elements of Group 15: Nitrogen family: elements are nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi) that belong to the configuration is ns2np3.
  • Atomic and ionic radii:
  1. Increased covalent and ionic groups are prepared. 
  2. There is an appreciable increase in the covalent radii from N to P. 
  3. There is a slight increase in As to Bi due to the presence of filled d and f orbitals in heavy elements.
  •  Ionization energy:
  1. It reduces the group due to the increase in atomic size. 
  2. Due to the small size of group 14 elements, group 15 elements have higher ionization energy than group 14 elements. 
  3. Group 15 elements have higher ionization energies than group 16 elements because they have a stable electronic configuration, ie, half-filled P-orbitals.
  4. Allotropy:  Except nitrogen, all other elements of group 15 show allotropy.
  5. Catenation: Nitrogen exhibits a certain degree of catalysis due to the triple bond but phosphorus shows a maximum caption. The tendency to show citations is lower down the group.
  • Oxidation states
  1. Oxidation states that are common +3, +5 and –3.
  2. The tendency of the oxidation state-3 to appear in the group decreases due to the decrease in electrical mobility due to the increase in the size of the atom.


  • Reactivity towards hydrogen:
  1. They are trihydrates, MH3.
  2. Belongs to sp3  hybridization.
  3. The stability of hydrides in the group is reduced by the decrease in the bond dissociation energy in the group.

NH3> PH3> AsH3> SbH3> BiH3            

  • Boiling point:

PH3 < AsH3 < NH3 < SbH3 < BiH3

The boiling point increases with the increase in the size of the van der Waals forces.

  • Bond angle:

Electronegativity N is the highest. Consequently, the single pairs will be oriented towards nitrogen and, will be more strongly repelled between the pairs of bonds. Therefore, there is the highest bond angle. After nitrogen, electronegativity decreases in the group.

  • Reactivity towards oxygen:
  1. All trioxides group 15 elements generated from (M2O3) and pent oxides (M2O5).
  2. As we move down the group, the atomic size increases and, therefore, the acidic value of the oxide decreases, and the radical bottom of the group increases.
  • Reactivity towards metals:  metal element reaction to form binary compounds within –3 oxidation states.
  • Anomalous behaviour of nitrogen:  Nitrogen behaviour differs from rest elements.
  • Reasons:
  1. Smaller size.
  2. Lack of d – orbitals 
  3. High electronegativity
  4. It has high ionization enthalpy
  • Dinitrogen:

          a) Preparation:

  • b) Physical Properties:  Colorless, Odorless, tasteless and non-toxic gas.
  • Ammonia: Trinomial pyramidal along with nitrogen atom at its apex. Constitute of 3 bond pairs with 1 lone pair.
  • Nitrogen (N) is sp3 hybridized.


              Haber’s process:

  • Nitric Acid:

Ostwald Process:  Nitric acid is a strong oxidizing agent in the concentrated as well as in the dilute state.


          Oxidation states:

  1. Oxygen does not show +6 oxidation states due to the absence of d – orbitals.
  2. Po does not show +6 oxidation states due to the inert torque effect. 
  3. The stability of the oxidation state -2 decreases due to the increase in atomic size and the decrease in electronegativity.
  • Ionization enthalpy:

            Ionization of the elements of group 15 is less than that of group 15, due to the half-filled p orbitals in group 15, which is more stable.

  • Reactivity with hydrogen:
  1. Elements of group 16 form hydrides.
  2. Have bent shape.
  • Acidic nature: H2O < H2S < H2Se < H2Te
    This is due to the H-E bond length  that increases down the group
  • Thermal stability
    This is due to the H-E bond length that increases down the group.
  • Reducing character
    H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
  • Reactivity with oxygen:  and EO3
  1. The renewable form of dioxide is reduced in the group because oxygen has a strong positive field which attracts the hydroxyl group and is easy to remove.
  2. Acidity decreases down the group.
  • Reactivity with halogens: EX2, EX4, and EX6

           Halides stability decreases: F – > Cl – > Br – > I –.

  1. The E-X bond length increases with an increase in size.

Oxygen: The compounds of oxygen and other elements are called oxides are the compounds of oxygen and other elements.

  • Types of oxides:

Ozone: Preparation: Prepared by silently passing electric discharge within pure and dry oxygen in which 10 to 15 % oxygen gets converted to ozone.

  • Sulfur:




  • Atomic and Ionic Radii: Halogens have the smallest atomic radii in their respective periods due to the maximum effective molecular charge. 
  • Ionization enthalpy: Due to their small size compared to other groups, they have a much higher ionization.
  • Electron gain enthalpy
  • Halogens have maximum negative electron gain enthalpy because these elements contain only one electron less than the stable configuration of the noble gas. 
  • The electron gain enthalpy becomes less negative under the group as the atomic size below the group increases. 
  • Electronegativity:
  1. These elements are highly electronegative and are below the electronegativity group. 
  2. They have a high effective nuclear charge.
  • Bond dissociation enthalpy:

Bond dissociation enthalpy follows the order: Cl2 > Br2 > F2 > l2, Due to the increase in bond length as per the size of the elements.

Discussion of Exercises of NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements


  • The 1st section of NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements has 37questions which are MCQs that will ask you to choose correct statements on acidic strength, enthalpy of vaporization, Haber’s process, etc.
  • The 2nd section has 21 questions which are short answer type questions that will help you to understand different experiments and theories of disproportionate reactions, Haber’s reaction, electron gain enthalpy, etc.
  • The 3rd section has 7 questions which are matching type questions that are a mixture of different terminologies based on properties of the p-block element in the periodic table.
  • The 4th section has 5 questions which are Assertion and Reason Type questions that are based on acidic reactions, rhombic monoclinic sulfur and less reactive metal elements of the periodic table.
  • The 5th section has 3 questions that are a long answer type which will ask you to support your answers with chemical reactions on reactivity series.
  • The NCERT exemplar questions include the simplest quality problems that will test you in varying levels of difficulty on any given topic. Questions that are mentioned within the NCERT exemplar are of immense importance from CBSE’s point of view.

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  • NCERT Exemplar Class 12 Chemistry Solutions Chapter 7- The p-Block Elements will help you to prepare well for the CBSE Class 12 Board exams
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  • We have followed all the guidelines of CBSE and followed the latest syllabus of CBSE Class 12 Chemistry
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