P Block Elements XII

Question 1

Molecular nitrogen comprises………% by volume of the atmosphere.

Answer 1

78

Question 2

Chile saltpetre

Answer 2

NaNO3

Question 3

Indian saltpetre

Answer 3

KNO3

Question 4

Phosphorus occurs in minerals of the apatite family

Answer 4

Ca9(PO4)6. CaX2 (X = F, Cl or OH)

Question 5

…………… is a synthetic radioactive element

Answer 5

Moscovium

Question 6

Statement 1: There is a considerable increase in covalent radius from N to P.
Statement 2: From As to Bi only a small increase in covalent radius is observed

Answer 6

Both are correct

Question 7

Assertion: The ionisation enthalpy of the group 15 elements is much greater than that of group 14 elements in the corresponding periods.

Answer 7

Reason: Because of the extra stable half-filled p orbitals electronic configuration and smaller size

Question 8

All the elements of this group are polyatomic.

Answer 8

Group 15

Question 9

In G15 except………all the elements show allotropy.

Answer 9

nitrogen

Question 10

Why does NO2 dimerise?

Answer 10

NO2 contains odd number of valence electrons. It behaves as a typical odd molecule. On dimerisation, it is converted to stable N2O4 molecule with even number of electrons

Question 11

The spontaneous combustion of……….. is technically used in Holme’s signals.

Answer 11

phosphine

Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved burn and serve as a signal. It is also used in smoke screens.

Question 12

Assertion: Bond angle in PH4+ is higher than that in PH3.

Answer 12

Reason: Both are sp3 hybridised. In PH4+ all the four orbitals are bonded whereas in PH3 there is a lone pair of electrons on P, which is responsible for lone pair-bond pair repulsion in PH3 reducing the bond angle to less than 109° 28’

Question 13

Assertion: PCl3 fumes in moisture

Answer 13

Reason: PCl3 hydrolyses in the presence of moisture giving fumes of HCl.

PCl3 + 3H2O ————> H3PO3 + HCl

Question 14

Are all the five bonds in PCl5 molecule equivalent?

Answer 14

PCl5 has a trigonal bipyramidal structure and the three equatorial P-Cl bonds are equivalent, while the two axial bonds are different and longer than equatorial bonds.

Question 15

Assertion: H3PO2 shows reducing behaviour

Answer 15

Reason: In H3PO2, two H atoms are bonded directly to P atom which imparts reducing character to the acid.

Question 16

Basicity of H3PO4

Answer 16

3

Question 17

Gypsum

Answer 17

CaSO4.2H2O

Question 18

Epsom salt

Answer 18

MgSO4.7H2O

Question 19

Baryte

Answer 19

BaSO4

Question 20

Galena
Zinc blende
Copper pyrites.

Answer 20

PbS

ZnS

CuFeS2

Question 21

Livermorium is a synthetic radioactive element. Its symbol is Lv, atomic number…….

Answer 21

116

Question 22

Polonium is radioactive and is short lived with Half-life…….. days

Answer 22

13.8

Question 23

Assertion: H2S is less acidic than H2Te

Answer 23

Reason: Due to the decrease in bond (E–H) dissociation enthalpy down the group, acidic character increases.

Question 24

Assertion: H2O is a liquid and H2S a gas

Answer 24

Reason: Because of small size and high electronegativity of oxygen, molecules of water are highly associated through hydrogen bonding resulting in its liquid state.

Question 25

Which form of sulphur shows paramagnetic behaviour?

Answer 25

In vapour state sulphur partly exists as S2 molecule which has two unpaired electrons in the antibonding π* orbitals like O2 and, hence, exhibits paramagnetism.

Question 26

How is the presence of SO2 detected ? (4) tests

Answer 26

Smell Test: SO₂ has a characteristic pungent, suffocating odor. Acidified Potassium Dichromate Test: Passing SO₂ through acidified potassium dichromate solution turns the orange solution green due to the reduction of Cr₂O₇²⁻ to Cr³⁺. Lime Water Test: Passing SO₂ through lime water (Ca(OH)₂) forms a white precipitate of calcium sulfite (CaSO₃), which dissolves upon excess SO₂ due to the formation of soluble calcium hydrogen sulfite. Potassium Permanganate Test: SO₂ decolorizes acidified potassium permanganate solution (purple to colorless) due to its reducing nature.

Question 27

Why is Ka2<<

Answer 27

H2SO4 is a very strong acid in water largely because of its first ionisation to H3O+ and HSO4- The ionisation of HSO4- to H3O+ and SO4 2- is very very small That is why Ka2 «Ka1

Question 28

Fluorine is present mainly as insoluble fluorides like

Answer 28

Fluorspar CaF2 Cryolite Na3AlF6 Fluoroapatite 3Ca3(PO4)2.CaF2

Question 29

Carnallite

Answer 29

KCl.MgCl2.6H2O

Question 30

Tennessine is a synthetic radioactive element. Its symbol is Ts, atomic number……..

Answer 30

117

Question 31

Half life of Ts is in milliseconds

Answer 31

True

Question 32

Assertion: Halogens have maximum negative electron gain enthalpy in the respective periods of the periodic table

Answer 32

Reason: Halogens have the smallest size in their respective periods and therefore high effective nuclear charge. As a consequence, they readily accept one electron to acquire noble gas electronic configuration.

Question 33

Assertion: Although electron gain enthalpy of fluorine is less negative as compared to chlorine, fluorine is a stronger oxidising agent than chlorine

Answer 33

Reason: It is due to (i) low enthalpy of dissociation of F-F bond (ii) high hydration enthalpy of F-

Question 34

Assertion: Fluorine exhibits only –1 oxidation state whereas other halogens exhibit + 1, + 3, + 5 and + 7 oxidation states also

Answer 34

Reason: Fluorine is the most electronegative element and cannot exhibit any positive oxidation state. Other halogens have d orbitals and therefore, can expand their octets and show + 1, + 3, + 5 and + 7 oxidation states also.

Question 35

Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy, compare the oxidising power of F2 and Cl2.

Answer 35

The electron gain enthalpy of chlorine is more negative than that of fluorine. However, the bond dissociation energy of fluorine is much lesser than that of chlorine. Also, because of its small size, the hydration energy of fluorine is much higher than that of chlorine. Therefore, the latter two factors more than compensate for the less negative electron gain enthalpy of fluorine. Thus, fluorine is a much stronger oxidizing agent than chlorine.

Question 36

Show the anomalous behaviour of fluorine.

Answer 36

The anomalous behaviour of fluorine is due to its small size, highest electronegativity, low F-F bond dissociation enthalpy, and non availability of d orbitals in valence shell. Ionisation enthalpy, electronegativity, and electrode potentials are all higher for fluorine than expected from the trends set by other halogens Ionic and covalent radii, m.p. and b.p., enthalpy of bond dissociation and electron gain enthalpy are quite lower than expected

Question 37

Assertion: Most of the reactions of fluorine are exothermic

Answer 37

Reason: Due to the small and strong bond formed by it with other elements

Question 38

……………. forms only one oxoacid while other halogens form a number of oxoacids.

Answer 38

Fluorine

Question 39

Assertion: Hydrogen fluoride is a liquid (b.p. 293 K)

Answer 39

Reason: It forms strong hydrogen bonding.

Question 40

Write the balanced chemical equation for the reaction of Cl2 with hot and concentrated NaOH. Is this reaction a disproportionation reaction?

Answer 40

3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O Yes, chlorine from zero oxidation state is changed to –1 and +5 oxidation states.

Question 41

Formulas for the following POISONOUS gases Phosgene Tear gas Mustard gas

Answer 41

COCl2 CCl3NO2 ClCH2CH2SCH2CH2Cl

Question 42

Give the reason for bleaching action of Cl2.

Answer 42

The bleaching action is due to oxidation It bleaches vegetable or organic matter in the presence of moisture. Bleaching effect of chlorine is permanent. Cl2 + H2O → 2HCl + O

Question 43

Assertion: When HCl reacts with finely powdered iron, it forms ferrous chloride and not ferric chloride.

Answer 43

Reason: Its reaction with iron produces H2. Fe + 2HCl————> FeCl2 + H2 Liberation of hydrogen prevents the formation of ferric chloride.

Question 44

………… has the lowest boiling point (4.2 K) of any known substance

Answer 44

Helium

Question 45

Assertion: Noble gases have very low boiling points

Answer 45

Reason: Noble gases being monoatomic have no interatomic forces except weak dispersion forces and therefore, they are liquefied at very low temperatures. Hence, they have low boiling points.

Question 46

March 1962 ……….. then at the University of British Columbia, observed the reaction of a noble gas.

Answer 46

Neil Bartlett

Question 47

Assertion: Helium is used in filling balloons for meteorological observations. Reason: Helium is a non-inflammable and light gas

Answer 47

Both are correct and correct explanation

Question 48

Liquid helium (b.p. 4.2 K) finds use as………. agent for carrying out various experiments at low temperatures

Answer 48

cryogenic

Question 49

……………. Is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis

Answer 49

Helium

Question 50

…………. is used in discharge tubes and fluorescent bulbs for advertisement display purposes

Answer 50

Neon

Question 51

Argon bulbs are used in botanical gardens and in green houses.

Answer 51

False Neon bulbs are used in botanical gardens and in green houses.

Question 52

Statement 1: There are no significant uses of Xenon and Krypton. Statement 2: They are used in light bulbs designed for special purposes.

Answer 52

Both correct

Question 53

Assertion: NH3 form hydrogen bond but PH3 does not

Answer 53

Reason: Nitrogen is highly electronegative as compared to phosphorus. This causes a greater attraction of electrons towards nitrogen in NH3 than towards phosphorus in PH3

Question 54

Assertion: NH3 is basic while BiH3 is only feebly basic.

Answer 54

Reason: Nitrogen has a small size due to which the lone pair of electrons is concentrated in a small region. This means that the charge density per unit volume is high, down a group, the size of the central atom increases and the charge gets distributed over a large area decreasing the electron density. Hence, the electron donating capacity of group 15 element hydrides decreases on moving down the group.

Question 55

Assertion: Nitrogen exists as a diatomic molecule and phosphorus as P4

Answer 55

Reason: Nitrogen being small in size forms a very stable diatomic molecule, N2. On moving down a group, the tendency to form pπ−pπ bonds decreases (because of the large size of heavier elements). Therefore, phosphorus (like other heavier metals) exists in the P4 state.

Question 56

Assertion: Nitrogen show catenation properties less than phosphorus

Answer 56

Reason: The relative weakness of the N−N single bond as compared to the P−P single bond. Since nitrogen atom is smaller, there is greater repulsion of electron density of two nitrogen atoms, thereby weakening the N−N single bond.

Question 57

Assertion: Fluorine forms only one oxoacid, HOF.

Answer 57

Reason: It has high electronegativity and small size.

Question 58

Which one of the following does not exist? (i) XeOF4 (ii) NeF2 (iii) XeF2 (iv) XeF6

Answer 58

NeF2 does not exist.

Question 59

Assertion: Noble gases have comparatively large atomic sizes

Answer 59

Reason: Noble gases do not form molecules. In case of noble gases, the atomic radii corresponds to van der Waal’s radii. On the other hand, the atomic radii of other elements correspond to their covalent radii. By definition, van der Waal’s radii are larger than covalent radii.

Question 60

Assertion: The hydrolysis of XeF6 lead to a redox reaction Reason: The products of hydrolysis are XeOF4 and XeO2F2 where the oxidation states of all the elements remain the same as it was in the reacting state.

Answer 60

Assertion is false and reason is true The hydrolysis of XeF6 doesn’t lead to a redox