NEET Questions Solved


The phenomenon in which polar crystals on heating produce electricity is called:-
(a) pyro-electricity
(b) piezo-electricity
(c) ferro-electricity
(d) ferri-electricity

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(a) It is the defination of pyro-electricity.

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Which arrangement of electrons leads to anti-ferromagnetism?
(a)  ↑↑↑↑
(b)  ↑↓↑↓
(c) Both (a) and (b)
(d) None of these

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(b) Anti-ferromagnetic possess complementary dipoles alignment giving net dipole moment equal to zero.

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A spinel is an important class of oxides consisting of two types of metal ions with the oxide ions arranged in ccp layers. The normal spinel has 1/8th of the tetrahedral void occupied  by one type of metal and one half of the octahedral voids occupied by another type of metal ions. Such a spinel is formed by Zn2+, Al3+ and O2- with Zn2+ in tetrahedral void. Give the simplest formula of the spinel.

(A) ZnAl2O4

(B) ZnAl2O3

(C) ZnAlO

(D) None of these

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(A) Let  the no. of tetrahedral voids = a

No. of octahedral voids = a/2

1/8 th tetrahedral voids is occupied by Zn2+

No. of Zn2+ =a/8

1/2 of octahedral voids occupied by Al3+

No. of Al3+ = a/4

Ratio of Zn2+: Al3+

             1     :   2

For 1 mole Zn2+, Al3+=2

Total +ve charge = 2+3x2=8  therefore, No. of O2- =4

The simplest formula will be  ZnAl2O4

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What type of substances would make better Permanent Magnets:

Ferromagnetic or Ferrimagnetic?

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Ferromagnetic substances would make batter permanent magnets

Example : Fe, Co, Ni etc.

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