Test: Magnetic & Electric Properties of Solids & Semiconductors (Old NCERT) - NEET MCQ

I. Mg (metal) conducts electricity in solid state as well as in molten state due to available free valence electrons.

II. TiO behaves like metals and is a good conductor of electricity.

III. I₂ is a bad conductor.

IV. H₂O (ice) is a bad conductor.

(a) When smaller cation migrates to interstitial site, it is called dislocation defect. It is also called Frenkel defect.

(b) When equal number of cation and anion are missing or one cation (A⁺) is missing and charge is balanced by A²⁺ , then this is called Schottky defect.

(c) as in (a)

(d) Electronic defects (n-type, p -type) is due to doping of impurity.

 (b)

(a) When Si is doped with electron-deficient impurity -(p -type)

(b) When Si is doped with electron-rich impurity-(n-type)

(c) In case of semiconductors, the gap between the valence band and conduction band is small. Some electrons may Jump to conduction band and thus, conduction is observed. Semiconductors of this type are called intrinsic semiconductors.

(d) Insulators are non-conducting with high energy gap.

 (c)

When polar crystal is subjected to a mechanical stress, electricity is produced. It is called piezoelectricity.

Piezoelectric crystals with permanent dipoles (domains aligned in ! same direction) are said to have ferroelectricity as in (a) and with : zero dipoles (domains aligned equally in opposite direction) are said to have anti-ferroelectricity as in (b).

Metals are good conductors of electricity and have conductivities in the order 10⁷(Ωm^-1) or 10⁵(Ωm-1).
Insulator: Solids having range of conductivity from 10^-20 to 10^-10 ohm^-1 m^-1 are considered as insulators.
Semiconductor: Solids having intermediate range of conductivity, i.e. from 10^-6 to 10⁴ ohm^-1 m^-1 are called semiconductors.

Electrons in 3 s orbital in one sodium atom (conduction band) = 1

Thus, total conduction bands (energy levels = 

Ti₂O₃, conducting below 41OK and insulating at about 150 K

 (a,b) When Si or Ge is doped with a group 13 elements (B, Al, Ga) then, one valence electron of Si makes a hole or vacancy. When electric field is applied, electrons move towards positively charged plate through electronic holes. It would appear that electronic holes are positively charged and are moving towards negatively charged plate.

 (a,b,c,d)

Si ( 1 4 ) - [Ne] 3s² 3p² (group 14 element having four valence electrons). Thus, each atom of Si is covalently bonded to four neighbouring atoms.

 3 (five valence electrons

Group 15 elements Four electrons are involved in bonding with | four electrons of Si and one remaining electron becomes I delocalised and increases the conductivity of Si. Thus, increase in I the conductivity is due to doped negatively charged electron. This is called n-type semiconductor.

Group 13 elements

[B, Al, Ga] ns²np¹ In this case, B, Al or Ga is short of one electron (as compared to Si). This is called electron hole or electron vacancy. Under the influence of electric field, electron hole moves towards the positively charged plate and is called p -type semiconductor.

The correct answer is option C
TiO3​ behaves as conductor or insulator depending on temperature because of a variation of energy gap between valence band and conduction band with the variation of temperature.

n = 0, Magnetic moment = 0

Thus, (a) is correct.

(b) Paramagnetic substances are magnetised in a magnetic field in the same direction hence, weakly attracted thus, (b) is correct.

(c) Ferromagnetic substances can be magnetised permanently, thus, given statement is incorrect.

(d) Substances like MnO showing anti-ferromagnetism have domain structure similar to ferromagnetic substances, but their domains are oppositely oriented and cancel out each other's magnetic moment.

 (a,b)

I and III have been doped with pentavalent impurity (P and As). There is one surplus electron and this results in the formation of n-type semiconductor. Surplus electron is responsible for conduction. II and IV have been doped with trivalent impurity (B and Al).
There is one electron short for bonding with Ge, hence a hole is formed. Hole moves through the electric field. This is p-type semiconductor.

. (b)

Graphite has four valence electron

Three electrons are involved in covalent bonding with neighbouring atoms giving it a hexagonal type packing (layers) such that one layer can slide over the other. The fourth electron makes the graphite conducting. Hexagonal sheets are with sp2- hybridised carbon.
Thus, both Statements I and II are correct but Statement II is not the correct explanation of Statement I.

(a)

In solid state, metal ions of ferromagnetic substances are grouped together into small regions called domains. Each domain acts as a tiny magnet. In an unmagnetised ferromagnetic substance, domains are randomly oriented and their magnetic moments are cancelled. In a magnetic field, all the domains are oriented in the direction of the magnetic field producing a strong magnetic effect and magnetism persists permanently even after magnetic field is removed.

Thus, both Statements I and II are correct and Statement II is the correct explanation of Statement I

 (c)

Anti-ferrom agnetic substances (as MnO) have following domain arrangements

following domain arrangements.

These domains are oppositely oriented and cancel out each other's magnetic moment and making it zero (even in the absence of magnetic field).
Thus, Statement I is correct and Statement II is incorrect.

 (b)

Increase in temperature causes thermal agitation of metal ions and thus, electrical conductivity is decreased. Thus, Statement I is correct. In the presence of electric field, flow of electrons is impeded. Thus, Statement II is correct but is not the correct explanation of Statement I.

 (b) Sem iconductors have small energy g ap between conduction band and valence band

On increasing temperature, electron from valence band can jump to conduction band and thus, electrical conductivity is increased. Thus, both Statements I and II are correct but Statement II is not the correct explanation of Statement I.

(i) Si doped with As has one extra electron for conduction, thus n-type semiconductor.

(ii) Ge doped with B has short of one electron thus, a hole is formed, thus a p-type semiconductor.

(iii) Metals have sea of electrons responsible for electronic conduction.

Electron flow is due to electrolysis. Thus, electrolytic conduction.
Thus, (i) (s),

(ii) -> (r),

(iii) -» (q),

(iv) (p).

P indicates that bonding molecular orbitals are empty.

Q indicates that bonding molecular orbitals are filled.

R indicates that bonding and antibonding molecular orbitals are filled.

Highest melting point is for the metal having filled bonding molecular orbitals (they have maximum bond order). Lowest melting point is for the metal having filled bonding and anti-bonding molecular orbitals thus, bond order is zero. Increasing order of hardness of the metals is R < P< Q

Hardness increases with increasing bond order.

P indicates that bonding molecular orbitals are empty.

Q indicates that bonding molecular orbitals are filled.

R indicates that bonding and antibonding molecular orbitals are filled.

Highest melting point is for the metal having filled bonding molecular orbitals (they have maximum bond order). Lowest melting point is for the metal having filled bonding and anti-bonding molecular orbitals thus, bond order is zero. Increasing order of hardness of the metals is

R < P< Q

Hardness increases with increasing bond order.

(5)

Species with atieast one or more unpaired electron(s) are attracted by the magnetic field and is said to be paramagnetic.

No unpaired electron hence, diamagnetic.

O₂ - Two unpaired electrons in anti bonding molecular orbitals.

Fe²⁺ - Four unpaired electrons in 3d-orbital.

Cr³⁺ - Three unpaired electrons in 3c/-orbital.

Cu⁺ - One unpaired electron in 3d-orbital.

O^-₂ One unpaired electron in antibonding molecular orbitals.

where, n = number of unpaired electrons

Diamagnetic substance have all paired electron.
(a) [Fe(CN)₆​]³⁻Oxidation state of Fe=+3
It has one unpaired electron and is paramagnetic.
(b) NiCl₄^2−​ - It has two unpaired electrons and is paramagnetic
(c) [Ni(CO)₄​] - It has no unpaired electron and is diamagnetic
(d) [MnCl₄​]²⁻ - It is paramagnetic as it has five unpaired electrons.

 (9) Antiferromagnetism arises when net dipole alignment is zero due to equal and opposite alignment. This is observed in

MnO, MnO₂, Mn₂O, FeO, Fe₂O₃, NiO ,Cr₂O₃, CoO, Co₃O₄.