Online Test — Structure of the Atom
18 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 18
The electron was discovered by:
Goldstein
Thomson
Chadwick
Rutherford
Explanation: J. J. Thomson discovered the electron from cathode-ray experiments.
Question 2 of 18
The charge on a proton is:
-1
0
+1
+2
Explanation: The proton carries a unit positive charge of +1.
Question 3 of 18
The neutron has:
a positive charge
a negative charge
no charge
a double charge
Explanation: The neutron is electrically neutral, with mass about 1 u.
Question 4 of 18
In Thomson's model the atom is like a:
solar system
plum pudding
ladder
single point
Explanation: Thomson pictured a positive sphere with electrons embedded, like plums in a pudding.
Question 5 of 18
Rutherford's experiment used a thin foil of:
aluminium
gold
iron
copper
Explanation: Rutherford bombarded a thin gold foil with alpha particles.
Question 6 of 18
Most alpha-particles passing straight through the foil showed that the atom is:
solid
mostly empty space
negatively charged
very heavy throughout
Explanation: Undeflected passage of most particles means the atom is largely empty space.
Question 7 of 18
The main drawback of Rutherford's model was that it could not explain the atom's:
colour
stability
size
charge
Explanation: Revolving electrons should radiate energy and spiral into the nucleus, so it could not explain stability.
Question 8 of 18
The maximum number of electrons in the K shell is:
2
8
18
32
Explanation: By 2n², the K shell (n = 1) holds 2 × 1² = 2 electrons.
Question 9 of 18
The maximum number of electrons in any outermost shell is:
2
8
18
32
Explanation: The outermost shell can hold at most 8 electrons (octet).
Question 10 of 18
The electronic configuration of chlorine (Z = 17) is:
2, 8, 7
2, 7, 8
8, 8, 1
2, 8, 8
Explanation: Filling K (2), L (8) leaves 7 for the M shell: 2, 8, 7.
Question 11 of 18
The electronic configuration of calcium (Z = 20) is:
2, 8, 10
2, 8, 8, 2
2, 18
2, 10, 8
Explanation: M stops at 8 (outermost rule) and the last two electrons begin N: 2, 8, 8, 2.
Question 12 of 18
The valency of oxygen (2, 6) is:
6
2
8
0
Explanation: Oxygen has 6 valence electrons, so valency = 8 − 6 = 2.
Question 13 of 18
The atomic number of an element equals the number of:
neutrons
nucleons
protons
shells
Explanation: Atomic number Z is the number of protons in the nucleus.
Question 14 of 18
If Z = 11 and A = 23, the number of neutrons is:
11
12
23
34
Explanation: Neutrons = A − Z = 23 − 11 = 12.
Question 15 of 18
Atoms with the same atomic number but different mass numbers are:
isobars
isotopes
ions
isomers
Explanation: Isotopes have the same Z but different A (same protons, different neutrons).
Question 16 of 18
Which pair are isobars?
¹H and ²H
³⁵Cl and ³⁷Cl
⁴⁰Ca and ⁴⁰Ar
²³Na and ²⁴Na
Explanation: ⁴⁰Ca (Z=20) and ⁴⁰Ar (Z=18) are different elements with the same mass number 40.
Question 17 of 18
The isotope used to treat goitre / thyroid disorders is:
Uranium-235
Cobalt-60
Iodine-131
Carbon-14
Explanation: Iodine-131 is used to treat goitre and diagnose thyroid problems.
Question 18 of 18
The atomic mass of chlorine is 35.5 u (a fraction) because:
chlorine has half a proton
it is a weighted average of its isotopes
neutrons weigh 0.5 u
of an error in measurement
Explanation: Natural chlorine mixes ³⁵Cl and ³⁷Cl, so its atomic mass is their weighted average, 35.5 u.