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Chemistry Practice Questions

NCERT Class IX Chapter 4: Structure of the Atom

Created & Curated By S.K. Sinha

Section A: Questions
Q1.
The number of protons in the nucleus of an atom of an element having atomic number 17 is:
(A) 17
(B) 18
(C) 35
(D) 8
Q2.
Rutherford's Ī±-particle scattering experiment led to the discovery of:
(A) Electron
(B) Proton
(C) Nucleus
(D) Neutron
Q3.
The maximum number of electrons that can be accommodated in the L shell is:
(A) 2
(B) 8
(C) 18
(D) 32
Q4.
An atom has electronic configuration 2, 8, 7. What is the atomic number of this element?
(A) 2
(B) 8
(C) 17
(D) 7
Q5.
Which of the following correctly represents the electronic distribution in the Mg atom?
(A) 3, 8, 1
(B) 2, 8, 2
(C) 1, 8, 3
(D) 8, 2, 2
Q6.
The mass number of an atom is 23 and atomic number is 11. The number of neutrons is:
(A) 11
(B) 12
(C) 23
(D) 34
Q7.
Thomson's model of atom is also known as:
(A) Nuclear model
(B) Planetary model
(C) Plum pudding model
(D) Cubic model
Q8.
The valency of an element having electronic configuration 2, 8, 1 is:
(A) 1
(B) 2
(C) 3
(D) 8
Q9.
Which of the following statements about cathode rays are correct?
(i) They are negatively charged
(ii) They are deflected by electric field
(iii) They travel in straight line
(iv) They have negligible mass
(A) (i) and (ii)
(B) (i), (ii) and (iii)
(C) All of the above
(D) (i) and (iv)
Q10.
The K shell of an atom has:
(A) 1 electron
(B) At most 2 electrons
(C) 8 electrons
(D) 18 electrons
Q11.
The electronic configuration of an element is 2, 8, 8, 1. The element belongs to:
(A) 2nd period
(B) 3rd period
(C) 4th period
(D) 1st period
Q12.
Which of the following atoms will have the same mass number?
Atom A: 17 protons, 18 neutrons
Atom B: 18 protons, 17 neutrons
Atom C: 16 protons, 19 neutrons
(A) A and B
(B) A and C
(C) B and C
(D) All have different mass numbers
Q13.
In Rutherford's experiment, most of the Ī±-particles passed through the gold foil because:
(A) Gold foil is very thin
(B) Most of the space in an atom is empty
(C) Ī±-particles are very small
(D) Ī±-particles are positively charged
Q14.
The number of valence electrons in a chlorine atom (atomic number 17) is:
(A) 5
(B) 6
(C) 7
(D) 8
Q15.
An element X has mass number 35 and has 17 electrons in its atom. What will be the number of neutrons in the element?
(A) 17
(B) 18
(C) 35
(D) 52
Q16.
The first shell (K shell) can hold a maximum of:
(A) 2 electrons
(B) 8 electrons
(C) 18 electrons
(D) 32 electrons
Q17.
Which of the following has the electronic configuration 2, 8, 8, 2?
(A) 20Ca
(B) 24Mg
(C) 40Ar
(D) 39K
Q18.
The relative charge of proton is:
(A) +1
(B) -1
(C) 0
(D) +2
Q19.
Which of the following is NOT a characteristic of anode rays?
(A) They are positively charged
(B) They travel in straight lines
(C) They are deflected by magnetic field
(D) They have the same charge to mass ratio for different gases
Q20.
The maximum number of electrons that can be accommodated in the outermost shell is:
(A) 2
(B) 8
(C) 18
(D) 32
Q21.
An atom of an element has 2 electrons in the K shell, 8 electrons in the L shell and 6 electrons in the M shell. The atomic number of the element is:
(A) 6
(B) 8
(C) 16
(D) 18
Q22.
The nucleus of an atom contains:
(A) Protons only
(B) Neutrons only
(C) Protons and neutrons
(D) Protons, neutrons and electrons
Q23.
Isotopes of an element have:
(A) Same mass number
(B) Same number of neutrons
(C) Same atomic number
(D) Different number of electrons
Q24.
If the K and L shells of an atom are full, then what would be the total number of electrons in the atom?
(A) 2
(B) 8
(C) 10
(D) 18
Q25.
The atomic models given by different scientists are arranged in chronological order as:
(A) Dalton ā†’ Thomson ā†’ Rutherford ā†’ Bohr
(B) Thomson ā†’ Dalton ā†’ Rutherford ā†’ Bohr
(C) Rutherford ā†’ Thomson ā†’ Dalton ā†’ Bohr
(D) Bohr ā†’ Rutherford ā†’ Thomson ā†’ Dalton
Section B: Answers
Question Answer
Q1 (A)
Q2 (C)
Q3 (B)
Q4 (C)
Q5 (B)
Q6 (B)
Q7 (C)
Q8 (A)
Q9 (C)
Q10 (B)
Q11 (C)
Q12 (A)
Q13 (B)
Q14 (C)
Q15 (B)
Q16 (A)
Q17 (A)
Q18 (A)
Q19 (D)
Q20 (B)
Q21 (C)
Q22 (C)
Q23 (C)
Q24 (C)
Q25 (A)
Section C: Solutions
Q1.
Atomic number = number of protons = 17.
Q2.
Deflection of Ī±-particles revealed dense, positively charged nucleus.
Q3.
L shell (n=2) can hold maximum 2nĀ² = 2(2)Ā² = 8 electrons.
Q4.
Total electrons = 2 + 8 + 7 = 17; atomic number = 17.
Q5.
Mg has 12 electrons: K=2, L=8, M=2.
Q6.
Neutrons = Mass number - Atomic number = 23 - 11 = 12.
Q7.
Thomson's model: positive sphere with embedded electrons (plum pudding).
Q8.
Outermost shell has 1 electron; valency = 1.
Q9.
Cathode rays have all mentioned properties: negative charge, deflection, straight path, negligible mass.
Q10.
K shell (n=1) holds maximum 2nĀ² = 2(1)Ā² = 2 electrons.
Q11.
4 shells occupied; element belongs to 4th period.
Q12.
Mass number = protons + neutrons; A: 17+18=35, B: 18+17=35. Same mass number.
Q13.
Atoms are mostly empty space; Ī±-particles pass through undeflected.
Q14.
Cl (17): 2, 8, 7; outermost shell has 7 valence electrons.
Q15.
Neutral atom: protons = electrons = 17; neutrons = 35 - 17 = 18.
Q16.
First shell (K) capacity = 2nĀ² = 2(1)Ā² = 2 electrons maximum.
Q17.
Total electrons = 20; Ca has atomic number 20 with configuration 2,8,8,2.
Q18.
Proton carries +1 elementary charge relative to electron.
Q19.
Anode rays have different charge/mass ratios for different gases (depend on gas used).
Q20.
Outermost shell follows octet rule; maximum 8 electrons (except K shell).
Q21.
Total electrons = 2 + 8 + 6 = 16; atomic number = 16.
Q22.
Nucleus contains positively charged protons and neutral neutrons only.
Q23.
Isotopes have same atomic number (same protons) but different mass numbers.
Q24.
K shell: 2 electrons, L shell: 8 electrons; total = 10.
Q25.
Historical order: Dalton (1803) ā†’ Thomson (1897) ā†’ Rutherford (1911) ā†’ Bohr (1913).

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