Structure of atoms class9 Science Multiple Choice questions

Given below are the CBSE Structure of atoms class9 Science Multiple Choice questions(MCQ)

Multiple Choice Questions:

Question 1.
When a B-particle is emitted, the atomic number of daughter element is one unit more as compared to that of parent element. This increase in atomic number is due to:
(a) Addition of a proton to the nucleus
(b) Removal of an electron from the nucleus
(c) Decay of neutron present in the nucleus
(d) Any one of the above

Question 2.
What is an electron?
(a) A wave
(b) A particle
(c) Either of two, depending on how it is observed
(d) Neither of these

Question 3.
The work function of a metal is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from the metal is approximately:
(a) 540nm
(b) 400 nm
(c) 300 nm
(d) 220 nm

The cathode ray experiment was done for the first time by:
(a) J.J. Thomson
(b) John Dalton
(c) Goldstein
(d) Rutherford

Question 6.
The charge on an electron is:
(a) 1.6 x 10-6 coulombs
(b) 1.6 x 10-20 coulombs
(c) 1.6 x 10-19 coulombs
(d) 1.6 x 10-16 coulombs

Question 7.
The nucleus of an atom contains:
(a) Protons
(b) Electrons
(c) Protons and neutrons
(d) Neutrons

Question 8.
By whom was neutron discovered?
(a) Bohr
(b) Chadwick
(c) Rutherford
(d) Dalton

Question 9.
In an atom valence electron are present in:
(a) Outermost orbit
(b) Next to outermost orbit
(c) First orbit
(d) Any one of its orbit

Question 10.
The maximum number of electrons that can be accommodated in third shell ( n = 3) is:
(a) 2
(b) 8
(c) 18
(d) 10

Question 11.
In an atom, the constituent electrons:
(a) Do not move
(b) Are uniformly distributed
(c) Move around the nucleus in fixed energy levels.
(d) Move around the nucleus in a random way.

Question 12.
What is the number of valence electrons of AI?
(a) 1
(b) 2
(c) 3
(d) 4

Question 13.
Which of the following arrangements of electrons represent magnesium (Mg)?
(a) 2, 8, 1
(b) 2, 8, 2
(c) 2, 8, 3
(d) 2, 8, 4

Question 14.
Which of the following statements is incorrect for cathode rays?
(a) They move in straight line
(b) Their nature depends upon the nature of gas present in the discharge tube.
(c) They cost shadow of solid objects placed in their path
(d) They get deflected towards positive charge.

Question 15.
The isotopes of an element have:
(a) Same number of neutrons
(b) Same atomic number
(c) Same mass number
(d) None of these

Question 16.
Which of the following statements is not correct for Bohr’s model of an atom?
(a) The nucleus of an atom is situated at ts centre
(b) The electrons move in circular orbits
(c) Electrons jumps from one orbit to another
(d) An electron neither loses nor gains energy it jumps from one orbit to another.

Question 17.
The atomic number of an element is 11 ad its mass number is 23. The correct order representing the number of electrons, protons and neutrons respectively in this atom is:
(a) 11, 11, 12
(b) 11, 12, 11
(c) 12, 11, 11
(d) 23, 11, 23

Question 18.
Which of the following pairs are isotopes?
(a) Oxygen and ozone
(b) Ice and steam
(c) Nitric oxide and nitrogen dioxide
(d) Hydrogen and deuterium

Question 19.
Which of the following have equal number of neutrons and protons?
(a) Hydrogen
(b) Deuterium
(c) Fluorine
(d) Chlorine

Question 20.
The number of electrons in an element with atomic number X and atomic mass Y will be:
(a) (X - Y)
(b) (Y - X)
(c) (X + Y)
(d) X

Question 21.
The relative atomic masses of many elements are not whole numbers because:
(a) They cannot be determined accurately
(b) The atoms ionize during determination of their masses
(c) Existence of isotopes
(d) Presence of impurities

Question 23.
Which of the following has a charge of +1 and a mass of 1 amu?
(a) A neutron
(b) A proton
(c) An electron
(d) A helium nucleus

Question 24.
Which of the following describes an isotope with a mass number of 99 that contains 56 neutrons in its nucleus?
(a) 99Ba56
(b) 43Ba56
(c) 99Tc43
(d) 56Tc43

Which of the following isotopes is used as the standard for atomic mass?
(a) 12C
(b) 16O
(c) 13C
(d) 1H

Question 26.
Which f the following is not a basic particle of an element?
(a) An atom
(b) A molecule
(c) An ion
(d) None

Question 27.
Which would be the electrical charge on a sulphur atom containing 18 ellectrons?
(a) 2-
(b) 1-
(c) 0
(d) 2+

Question 28.
Which of the following pairs are isotopes?
(a) Oxygen and ozone
(b) Ice and steam
(c) Nitric oxide and nitrogen dioxide
(d) Hydrogen and deuterium

Question 29.
Members of which of the following have similar chemical properties?
(a) Isotope
(b) Isobars
(c) Allotropes
(d) Both isotopes and allotropes

Question 30.
A natural phenomenon that supports the experimental conclusion that atoms are divisible is:
(a) Allotropy
(b) Radioactivity
(c) Cracking
(d) None of these

Question 31.
Aluminum has a valence of 3 and sulphate has valence of 2. Therefore, the correct formula for aluminum sulphate is:
(a) AL2S2O4
(b) AL2 (SO4)3
(c) AL3 (SO4)2
(d) ALSO4

Question 32.
The correct representation of 3 molecules of chlorine is:
(a) 6 CI
(b) 3 Cl2
(c) 2Cl3
(d) Cl6

Question 33.
While performing cathode ray experiments, it was observed that there was no passage of electric current under normal conditions. Which of the following can account for this observation?
(a) Dust particles are present in air
(b) Carbon dioxide is present in air
(c) Air is a poor conductor of electricity under normal conditions
(d) One of the above

Question 34.
The fluorescence on the walls of discharge tube is due to:
(a) Cathode rays
(b) Anode rays
(c) Canal rays
(d) None of the above

Question 35.
Which of the following electronic configurations is wrong?
(a) Be (3) = 2, 1
(b) S (16) = 2, 6, 8
(c) P (15) = 2, 8, 5

Question 36.
5525Mn++ has:
(a) 25protons and 30neutrons
(b) 25neutrons and 25protons
(c) 25electrons and 40 protons
(d) None of the above

Question 37.
Which one of the following statement is not true?
(a) Most of the space in an atom is empty
(b) The total number of neutrons and protons is always equal in a neutral atom
(c) The total number of electrons and protons in an atom is always equal
(d) The total number f electrons in any energy level can be calculated by the formula 2n2

Question 38.
17Cl35 and 17Cl37 are examples of:
(a) Isobars
(b) Isotopes
(c) Isoelectrons atoms
(d) None of the above

Question 39.
How many electrons in a Hydrogen (H) atom:
(a) One
(b) Two
(c) Three
(d) Four

Question 40.
The orbital angular momentum of 2p electron is:
(a) 3h
(b) 6h
(c) Zero
(d) 2h/2n

Question 42.
The four quantum numbers that could identify the third 3p electron in sulphur are:
(a) N = 3, 1 = 0, m = +1, s = +1/2
(b) N = 2, 1 = 2, m = -1, s = -1/2
(c) N = 3, 1 = 2, m = +1, s = -1/2
(d) N = 3, 1 = 1, m = -1, s = +1/2

Question 43.
The atomic number of the element with maximum number of unpaired electrons is:
(a) 23
(b) 33
(c) 15
(d) 26

Question 44.
Which of the following orbital is more close to the nucleus?
(a) 5f
(b) 6d
(c) 7s
(d) 7p

Question 45.
The number of d- electrons in Fe2+ (Z = 26) is not equal to that of:
(a) s- electrons in Mg
(b) p- electrons in Ne
(c) d- electrons in Fe
(d) p- electros in CI

Question 47.
The correct setoff quantum numbers for the unpaired electron of scandium (Z = 21) is:
(a) 4, 2, 2, ±1/2
(b) 3, 2, -2, ±1/2
(c) 3, 1, 1, ±1/2
(d) 3, 2, 3, ±1/2

Question 49.
The shortest wavelengths of radiation emitted when can electron from infinity falls into the ionized H-atom(RH = 1.097 x 107 m-1)
(a) 91 nm
(b) 192 nm
(c) 406 nm
(d) 1.9 x 10-8 nm

Question 50.
13Al27 is a stable isotope. 13Al29 is expected to disintegrate by:
a.α emission
(b) β emission
(c) Positron emission
(d) Proton emission

Question 51.
n/p ratio of an element with atomic number greater tha 83 falls in the zone of instability. The element will undergo:
(a) α - decay
(b) β -decay
(c) β+ -decay
(d) No decay

Question 52.
Proton bombardment of Th230 followed by emission of two alpha particles produces:
(a) Rn232
(b) Fr223
(c) Ra223
(d) Fr222

Question 53.
In the radioactive decay:
The sequence of radiation emitted is:
(a) α, β, γ
(b) α, β α
(c) β, α, γ
(d) α, β β

Question 54.
Which of the following nuclides is least likely to be stable?
(a) 20C40
(b) 13ALsup>30
(c) 50Snsup>119
(d) 25Mnsup>55


This Class 9 Science MCQ for Structure of atoms with answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.

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