Vidaara.orgClass 8 · Mathematics
CodeVID-M8-WS
Atoms and Molecules — Practice Worksheet
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Choose the correct option (A, B, C or D) for each question.
- The answer key is at the end — try the paper first!
Section A — Multiple Choice (1 mark each)
25 × 1 = 25 marks
1.
The smallest particle of an element that can take part in a chemical reaction is the:
- A.Molecule
- B.Atom
- C.Mixture
- D.Compound
2.
The first scientific atomic theory was given by:
- A.Newton
- B.Dalton
- C.Ohm
- D.Faraday
3.
According to Dalton, atoms combine in:
- A.Random amounts
- B.Simple whole-number ratios
- C.Decimals
- D.Halves only
4.
A limitation of Dalton's theory is that atoms are actually:
- A.Indivisible
- B.Made of smaller particles
- C.Created easily
- D.All identical
5.
Atoms of the same element with different masses are called:
- A.Molecules
- B.Isotopes
- C.Ions
- D.Mixtures
6.
Which subatomic particle carries a positive charge?
- A.Electron
- B.Proton
- C.Neutron
- D.Photon
7.
The particle with no charge, found in the nucleus, is the:
- A.Proton
- B.Electron
- C.Neutron
- D.Ion
8.
The atomic number (Z) of an atom is the number of:
- A.Neutrons
- B.Protons
- C.Electrons + neutrons
- D.Shells
9.
The mass number (A) is equal to:
- A.Protons only
- B.Protons + neutrons
- C.Electrons only
- D.Neutrons − protons
10.
For $^{23}_{11}Na$, the number of neutrons is:
- A.11
- B.12
- C.23
- D.34
11.
Isotopes are atoms of the same element with the same atomic number but different:
- A.Number of electrons
- B.Mass numbers
- C.Charges
- D.Chemical properties
12.
The three isotopes of hydrogen differ in their number of:
- A.Protons
- B.Electrons
- C.Neutrons
- D.Shells
13.
Isotopes of an element have the same ______ properties.
- A.Physical
- B.Chemical
- C.Magnetic
- D.Electrical
14.
Carbon-14 is an isotope used for:
- A.Cooking
- B.Carbon dating
- C.Lighting
- D.Welding
15.
Atoms of different elements with the same mass number are called:
- A.Isotopes
- B.Isobars
- C.Isotones
- D.Ions
16.
The shells in which electrons are arranged are named, from the innermost:
- A.A, B, C
- B.K, L, M
- C.X, Y, Z
- D.1, 2, 3 only
17.
The maximum number of electrons in the K shell is:
- A.2
- B.8
- C.18
- D.32
18.
The electrons in the outermost shell are called:
- A.Core electrons
- B.Valence electrons
- C.Neutrons
- D.Protons
19.
The electronic configuration of sodium (Z = 11) is:
- A.2, 8, 1
- B.2, 8, 8
- C.8, 2, 1
- D.2, 9
20.
The combining capacity of an atom is called its:
- A.Valency
- B.Mass number
- C.Atomic number
- D.Density
21.
The smallest particle of a substance that can exist independently is a:
- A.Proton
- B.Atom
- C.Molecule
- D.Neutron
22.
The molecular formula H₂O shows that water has 2 hydrogen atoms and:
- A.2 oxygen atoms
- B.1 oxygen atom
- C.3 oxygen atoms
- D.no oxygen
23.
The molecular mass of a substance is the sum of the ______ of its atoms.
- A.Charges
- B.Atomic masses
- C.Volumes
- D.Valencies
24.
Avogadro's number is:
- A.6.022 × 10²³
- B.3.14
- C.9.8
- D.100
25.
One mole of a substance has a mass equal to its molecular mass in:
- A.Kilograms
- B.Grams
- C.Litres
- D.Newtons
Answer Key
Section A — Multiple Choice (1 mark each)
- (B) Atom
- (B) Dalton
- (B) Simple whole-number ratios
- (B) Made of smaller particles
- (B) Isotopes
- (B) Proton
- (C) Neutron
- (B) Protons
- (B) Protons + neutrons
- (B) 12
- (B) Mass numbers
- (C) Neutrons
- (B) Chemical
- (B) Carbon dating
- (B) Isobars
- (B) K, L, M
- (A) 2
- (B) Valence electrons
- (A) 2, 8, 1
- (A) Valency
- (C) Molecule
- (B) 1 oxygen atom
- (B) Atomic masses
- (A) 6.022 × 10²³
- (B) Grams
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