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The formula for calcium oxide is:

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Important Questions on Atoms and Molecules

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The contribution to the total current in a semiconductor, due to electrons and holes are

0.75

and

0.25

respectively. The drift velocity of electrons is

\frac{3}{2}

times that of holes at this temperature. Then the ratio between electron concentration and hole concentration is

EASY

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

A unit cell of calcium fluoride has four calcium ions. The number of fluoride ions in the unit cell is

EASY

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The barrier potential of a p-n junction depends on:

(a)

type of semi-conductor material

(b)

amount of doping

(c)

temperature
Which one of the following is correct?

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

Among the following, which have highest melting point?

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

An element ‘P’ which belongs to

13 th

group of the periodic table and another element ‘Q’ belongs to

16 th

group. The formula of the compound formed if they react with each other is:

EASY

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

An intrinsic semiconductor is converted into

n

-type extrinsic semiconductor by doping it with:-

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The radius of

K^{+}

133 pm

and that of

{Cl}^{-}

181 pm

. The volume of the unit cell of

KCl

expressed in

10^{- 22} {cm}^{3}

is:

EASY

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

Which among the following is NOT a polar molecular solid ?

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The element ‘X’ has an electronic configuration

2, 8, 3 .

Element ‘Y’ has an electronic configuration

2, 8 7

. The chemical formula of the compound formed when they react is

HARD

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

Consider an ionic solid

MX

, with

NaCl

structure. Construct a new structure

(Z)

, whose unit cell is constructed from the unit cell of

MX

, following the sequential instructions given below. Neglect the charge balance.

(i)

Remove all the anions

(X)

, except the central one.

(ii)

Replace all the face centered cations

(M)

, by anions

(X)

(iii)

Remove all the corner cations

(M)

(iv)

Replace the central anion

(X)

, with cation

(M)

.

The value of

(\frac{n u m b e r o f a n i o n s}{n u m b e r o f c a t i o n s})

Z

is _____.

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

In the following circuit diagram, the current through the battery is

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

An element X with atomic number

13

combines with another element Y of atomic number

17

. The formula of the compound formed and the nature of the bond will be:

EASY

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

Glass is

HARD

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The cubic unit cell structure of a compound containing cation $M$ and anion $X$ is shown below. When compared to the anion, the cation has smaller ionic radius. Choose the correct statement(s).

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

Silicon doped with gallium forms

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

A compound formed by elements

X

and

Y

crystallises in the cubic structure, where

X

atoms are at the corners of a cube and

Y

atoms are at the centre of the body. The formula of the compounds is

EASY

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Match the following

List - I List-II
A) Metallic solid I) Carbon tetrachloride
B) Covalent solid II) Calcium fluoride
C) Molecular solid III) Copper
D) Ionic solid IV) Silicon carbide
V) Glass

The correct answer is

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

In calcium fluoride, having the fluorite structure, the coordination numbers for calcium ion

(C a^{2 +})

and fluoride ion

(F^{-})

are

HARD

Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

The formulae of an oxide of an element

M

MO

. The formulae of its phosphate is

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Science>Chemistry>Atoms and Molecules>Writing Chemical Formulae

A solution of a substance 'X' is used for whitewashing.

(a) Name the substance 'X' and write its formula.

(b) Write the reaction of the substance with water.

The formula for calcium oxide is:

Important Questions on Atoms and Molecules

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