44
MCQ (Multiple Correct Answer)
An excess of potassium ions makes KCl crystals appear violet or lilac in colour since .............. .
A
some of the anionic sites are occupied by an unpaired electron
B
some of the anionic sites are occupied by a pair of electrons
C
there are vacancies at some anionic sites
D
F-centres are created which impart colour to the crystals
45
MCQ (Multiple Correct Answer)
The number of tetrahedral voids per unit cell in NaCl crystal is
A
4
B
8
C
twice the number of octahedral voids
D
four times the number of octahedral voids
46
MCQ (Multiple Correct Answer)
Amorphous solids can also be called ............ .
A
pseudo solids
B
true solids
C
super cooled liquids
D
super cooled solids
47
MCQ (Multiple Correct Answer)
A perfect crystal of silicon (fig) is doped with some elements as given in the options. Which of these options shows n-type semiconductors?
A
B
C
D
48
MCQ (Multiple Correct Answer)
Which of the following statements are correct?
A
Ferrimagnetic substances lose ferrimagnetism on heating and become paramagnetic
B
Ferrimagnetic substances do not lose ferrimagnetism on heating and remain ferrimagnetic
C
Antiferromagnetic substances have domain structures similar to ferromagnetic substances and their magnetic moments are not cancelled by each other
D
In ferromagnetic substances, all the domains get oriented in the direction of magnetic field and remain as such even after removing magnetic field