MCQs Based On Class 12 Chemistry Chapter 7 The p-Block Elements
MCQ Questions for Class 12 Chemistry are prepared by the subjects experts according to the latest pattern. These MCQs are very important for students who wants to score well in CBSE Board Exam. These MCQs on chapter 7 The p-Block Elements will also help students in understanding the concepts very well.
Q.1. Among the 15th group elements, as we move from nitrogen to bismuth, the pentavalency becomes less pronounced and trivalency becomes more pronounced due to
(a) Non metallic character
(b) Inert pair effect
(c) High electronegativity
(d) Large ionization energy
Q.2. Which of the following statements is not correct for nitrogen?
(a) Its electronegativity is very high
(b) d-orbitals are available for bonding
(c) It is a typical non-metal
(d) Its molecular size is small
AnswerAns. (b) In case of nitrogen, d-orbitals are not available.
Q.3. Collectively the elements of group 15 are called –
(d) None of these
AnswerAns. (a) Collectively these elements are called pnicogens and their compound pniconides.
Q.4. Ionic radii (in Å) of As3+, Sb3+ and Bi3+ follow the order
(a) As3+ > Sb3+ > Bi3+
(b) Sb3+ > Bi3+ >As3+
(c) Bi3+ > As3+ > Sb3+
(d) Bi3+ > Sb3+ > As3+
AnswerAns. (d) Ionic radii increases down the group
Q.5. Which one of the following elements is most metallic ?
AnswerAns. (d) Metallic character increases down the group, Bi is most metallic
Q.6. Which of the follow group 15 element forms metallic bonds in elemental state ?
AnswerAns. (d) Bismuth forms metallic bonds in elemental state.
Q.7. The three important oxidation states of phosphorus are
(a) –3, +3 and +5
(b) –3, +3 and –5
(c) –3, +3 and +2
(d) –3, +3 and +4
AnswerAns. (a) –3, +3, +5
Q.8. Which of the following statement is incorrect for group 15 elements ?
(a) Order of ionization enthalpies is ΔiH1 < ΔiH2 < ΔiH3
(b) The boiling point and melting point increases from top to bottom in the group
(c) Dinitrogen is a gas while all others are solids
(d) All statements are correct
AnswerAns. (b) The melting point in group 15 increases upto arsenic and then decreases upto bismuth.
Q.9. Nitrogen is relatively inactive element because
(a) its atom has a stable electronic configuration
(b) it has low atomic radius
(c) its electronegativity is fairly high
(d) dissociation energy of its molecule is fairly high
AnswerAns. (d) N2 molecule contains triple bond between N atoms having very high dissociation energy (946 kJ mol–1) due to which it is relatively inactive.
Q.10. Which of the following has the highest pπ – pπ bonding tendency ?
AnswerAns. (a) Nitrogen due to small size is able to show pπ-pπ lateral overlap forming N≡N, rest elements due to bigger size are not able to show pπ-pπ lateral overlap.
Q.11. Pick out the wrong statement.
(a) Nitrogen has the ability to form pπ-pπ bonds with itself.
(b) Bismuth forms metallic bonds in elemental state.
(c) Catenation tendency is higher in nitrogen when compared with other elements of the same group.
(d) Nitrogen has higher first ionisation enthalpy when compared with other elements of the same group.
AnswerAns. (c) Catenation tendency is higher in phosphorus when compared with other elements of same group.
Q.12. Nitrogen forms N2, but phosphorus is converted into P4 from P, the reason is
(a) Triple bond is present between phosphorus atom
(b) pπ – pπ bonding is strong
(c) pπ – pπ bonding is weak
(d) Multiple bond is formed easily
Q.13. What causes nitrogen to be chemically inert ?
(a) Multiple bond formation in the molecule
(b) Absence of bond polarity
(c) Short internuclear distance
(d) High bond energy
Q.14. Pentavalence in phosphorus is more stable when compared to that of nitrogen even though they belong to same group. This is due to
(a) dissimilar electronic configuration
(b) due to presence of vacant d-orbitals
(c) reactivity of phosphorus
(d) inert nature of nitrogen
AnswerAns. (b) Phosphorous can achieve coordination number 5 due to vacant d atomic orbitals in valence shell which is not possible in nitrogen
Q.15. Which one has the lowest boiling point ?
Nitrogen can not expand its octet due to absence of d-orbitals.
Among hydrides of group-15 elements, the bond length increases from N – H to Bi – H with increasing size of element. Bi – H bond is longest and weakest, it can break more easily and evolve H2 gas which acts as the reducing agent.
Lewis basic nature of NH3 and PH3 molecules is due to the presence of lone pairs on N and Bi atoms, respectively. P atom is much larger than N atom and also has empty d orbitals. Electron density due to lone pair on P gets diffused because of the presence of d-orbitals and so the lone pair is not easily available for donation. Hence PH3 is less basic than NH3.
The single N—N bond is weaker than the single P—P bond because of high interelectronic repulsion of the non-bonding electrons, occurring due to the small bond length.
On moving down the group, the stability of +5 oxidation state decreases while +3 oxidation state
increases due to inert pair effect.
Thus +5 oxidation state of Bi is less stable and Bi(V) is a stronger oxidising agent.
Due to inert pair effect the stability of +5 oxidation state decreases down the group in group 15. Hence tendency to form pentahalide decreases down the group 15 of the periodic table.
In + 5 oxidation state charge/radius ratio is higher than that in + 3 oxidation state. Hence, +5 oxidation state has more polarising power than that of + 3 oxidation state and pentahalides (in O.S. + 5) are more covalent than trihalides.
NH3 molecules are held together by strong inter molecular hydrogen bonds whereas PH3 molecules are held together by weak van der Waals bonds. Thus, NH3 has a higher boiling point than PH3.
White phosphorus consists of discrete P4 molecules in which each phosphorus atom is tetrahedrally bonded to other three phosphorus atoms. So, white phosphorus is highly reactive. In red phosphorus, P4 molecules are linked in an extended chain structure. So, red phosphorus is much less reactive.
Oxygen molecules are held together by weak van der Waals’ forces because of the small size and high electronegativity of oxygen. Sulphur shows catenation and the molecule is made up of 8 atoms with strong intermolecular forces.
Hence, there is large dierence in the melting and boiling points of oxygen and sulphur.
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