History, Laws & Modern Periodic Table — MH-CET Chemistry MCQs with Solutions
Free MH-CET Chemistry History, Laws & Modern Periodic Table MCQs with step-by-step solutions (40 questions). Part of Classification of Elements and Periodicity. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — History, Laws & Modern Periodic Table · easy · theory
The modern periodic law states that the properties of elements are a periodic function of their:
A. Number of neutrons
B. Atomic mass
C. Density
D. Atomic number ✓ Correct
Solution: Moseley established that atomic number (Z), not atomic mass, is the fundamental property; properties repeat periodically with Z.
Q2 — History, Laws & Modern Periodic Table · easy · theory
Mendeleev's periodic law was based on the:
A. Density
B. Number of valence electrons
C. Atomic number
D. Atomic mass ✓ Correct
Solution: Mendeleev arranged elements in order of increasing atomic mass.
Q3 — History, Laws & Modern Periodic Table · easy · theory
Döbereiner's triads are groups of three elements in which the atomic mass of the middle element is approximately:
A. The arithmetic mean of the other two ✓ Correct
B. The sum of the other two
C. Double the lightest
D. The product of the other two
Solution: In a triad, m(middle) ≈ [m(1) + m(3)]/2.
Q4 — History, Laws & Modern Periodic Table · easy · theory
Newlands' law of octaves compared the repetition of properties (every 8th element) to:
A. Colours of light
B. Days of the week
C. Musical notes ✓ Correct
D. Planetary orbits
Solution: Every eighth element had similar properties, like the octaves in music.
Q5 — History, Laws & Modern Periodic Table · medium · theory
A limitation of Newlands' law of octaves was that it:
A. Used atomic number
B. Left gaps for undiscovered elements
C. Was valid only up to calcium (lighter elements) ✓ Correct
D. Predicted new elements
Solution: The octave pattern broke down beyond Ca; it also left no gaps for undiscovered elements.
Q6 — History, Laws & Modern Periodic Table · easy · theory
A major achievement of Mendeleev's table was that he:
A. Left gaps and correctly predicted properties of undiscovered elements (eka-aluminium, eka-silicon) ✓ Correct
B. Placed hydrogen correctly
C. Explained isotopes
D. Used atomic number
Solution: He predicted eka-aluminium (Ga) and eka-silicon (Ge) with remarkable accuracy.
Q7 — History, Laws & Modern Periodic Table · medium · theory
Mendeleev placed certain elements (like Co before Ni, Te before I) out of atomic-mass order because he prioritised:
A. Similarity of chemical properties ✓ Correct
B. Atomic number
C. Colour
D. Density
Solution: Some pairs were reversed to keep chemically similar elements together — an anomaly resolved by atomic number.
Q8 — History, Laws & Modern Periodic Table · medium · theory
Moseley's X-ray experiment showed that √ν is a linear function of the atomic number, establishing that the fundamental property of an element is its:
A. Density
B. Valency
C. Atomic mass
D. Atomic number ✓ Correct
Solution: Moseley: √ν = a(Z − b), proving Z is fundamental and correcting Mendeleev's mass-based anomalies.
Q9 — History, Laws & Modern Periodic Table · medium · theory
The underlying cause of periodicity in properties is the:
A. Change in nuclear charge only
B. Increase in atomic mass
C. Increase in the number of neutrons
D. Periodic recurrence of similar valence-shell electronic configurations ✓ Correct
Solution: Elements with similar outer electron configurations recur at regular intervals, so their properties repeat.
Q10 — History, Laws & Modern Periodic Table · easy · theory
The long form (modern) periodic table has:
A. 7 periods and 8 groups
B. 7 periods and 18 groups ✓ Correct
C. 8 periods and 18 groups
D. 6 periods and 16 groups
Solution: The long form has 7 horizontal periods and 18 vertical groups, arranged by atomic number.
Q11 — History, Laws & Modern Periodic Table · easy · theory
The period number of an element corresponds to the:
A. Number of protons
B. Group number
C. Number of valence electrons
D. Principal quantum number (n) of its outermost shell ✓ Correct
Solution: The highest principal quantum number of the valence shell equals the period number.
Q12 — History, Laws & Modern Periodic Table · easy · theory
Elements belonging to the same group have the same:
A. Number of neutrons
B. Number of valence electrons (similar valence-shell configuration) ✓ Correct
C. Atomic mass
D. Number of shells
Solution: Same group ⇒ same outer-shell configuration ⇒ similar chemical properties.
Q13 — History, Laws & Modern Periodic Table · medium · theory
The number of elements in the 1st, 2nd, 3rd, 4th periods are respectively:
A. 8, 8, 8, 8
B. 2, 8, 8, 18 ✓ Correct
C. 2, 8, 8, 8
D. 2, 8, 18, 18
Solution: Determined by the orbitals being filled: 2, 8, 8, 18, 18, 32.
Q14 — History, Laws & Modern Periodic Table · medium · theory
Lothar Meyer plotted a curve showing the periodicity of which property against atomic mass?
A. Density only
B. Electronegativity
C. Ionisation energy
D. Atomic volume ✓ Correct
Solution: Lothar Meyer's atomic-volume curve showed peaks (alkali metals) recurring periodically.
Q15 — History, Laws & Modern Periodic Table · medium · theory
The chief demerit of Mendeleev's table was the incorrect placement of:
A. The noble gases exclusively
B. The alkali metals
C. Only the halogens
D. Isotopes and the position of hydrogen ✓ Correct
Solution: Isotopes (same properties, different mass) had no separate place; H's position was ambiguous.
Q16 — History, Laws & Modern Periodic Table · hard · theory
In Moseley's relation √ν = a(Z − b), the term "b" is the:
A. Rydberg constant
B. Number of neutrons
C. Screening (shielding) constant ✓ Correct
D. Atomic mass
Solution: b is a screening constant; a is a proportionality constant depending on the spectral line.
Q17 — History, Laws & Modern Periodic Table · easy · numerical
In the triad Li (7), Na (23), K (39), the predicted atomic mass of Na from the triad rule is:
A. 46
B. 32
C. 23 ✓ Correct
D. 16
Solution: Mean of Li and K = (7 + 39)/2 = 23, matching Na.
Q18 — History, Laws & Modern Periodic Table · easy · numerical
For the triad Cl (35.5), Br (?), I (127), the atomic mass of Br predicted by the triad rule is about:
A. 46
B. 91.5
C. 162
D. 81 ✓ Correct
Solution: Mean = (35.5 + 127)/2 = 81.25 ≈ 80 (actual Br).
Q19 — History, Laws & Modern Periodic Table · easy · numerical
For the triad Ca (40), Sr (?), Ba (137), the predicted mass of Sr is:
A. 48.5
B. 177
C. 88.5 ✓ Correct
D. 97
Solution: Mean = (40 + 137)/2 = 88.5 ≈ 88 (actual Sr).
Q20 — History, Laws & Modern Periodic Table · medium · numerical
An element has the configuration 1s² 2s² 2p⁶ 3s² 3p⁵. Its period and group are:
A. Period 3, Group 17 ✓ Correct
B. Period 5, Group 3
C. Period 3, Group 15
D. Period 2, Group 17
Solution: Outermost n = 3 ⇒ period 3; 7 valence electrons (3s²3p⁵) ⇒ group 17.
Q21 — History, Laws & Modern Periodic Table · medium · numerical
An element with configuration [Ar] 4s² belongs to:
A. Period 2, Group 4
B. Period 3, Group 2
C. Period 4, Group 12
D. Period 4, Group 2 ✓ Correct
Solution: n = 4 ⇒ period 4; ns² with 2 valence electrons ⇒ group 2.
Q22 — History, Laws & Modern Periodic Table · easy · numerical
The element with atomic number 11 lies in:
A. Period 1, Group 3
B. Period 3, Group 1 ✓ Correct
C. Period 3, Group 11
D. Period 2, Group 1
Solution: Na: 1s²2s²2p⁶3s¹ ⇒ period 3, group 1.
Q23 — History, Laws & Modern Periodic Table · medium · numerical
Mendeleev's "eka-silicon" and "eka-aluminium" are the modern elements:
A. Silicon and Aluminium
B. Tin and Boron
C. Germanium and Gallium ✓ Correct
D. Carbon and Gallium
Solution: Eka-silicon = Ge, eka-aluminium = Ga — both predicted before discovery.
Q24 — History, Laws & Modern Periodic Table · medium · numerical
The element with atomic number 35 is located in:
A. Period 5, Group 17
B. Period 3, Group 17
C. Period 4, Group 17 ✓ Correct
D. Period 4, Group 15
Solution: Br: [Ar]3d¹⁰4s²4p⁵ ⇒ period 4, group 17.
Q25 — History, Laws & Modern Periodic Table · medium · numerical
The number of elements present in the 4th period is:
A. 10
B. 18 ✓ Correct
C. 32
D. 8
Solution: The 4th period fills 4s, 3d, 4p ⇒ 2 + 10 + 6 = 18 elements.
Q26 — History, Laws & Modern Periodic Table · medium · numerical
The element with atomic number 20 belongs to which block, period, and group?
A. s-block, Period 2, Group 4
B. s-block, Period 4, Group 2 ✓ Correct
C. d-block, Period 4, Group 2
D. p-block, Period 4, Group 2
Solution: Ca: [Ar]4s² ⇒ s-block, period 4, group 2.
Q27 — History, Laws & Modern Periodic Table · hard · numerical
For two elements, Moseley's √ν values are proportional to (Z − 1). If Z = 13 gives √ν = k·12, then Z = 25 gives:
A. k·24 ✓ Correct
B. k·25
C. k·12
D. k·13
Solution: √ν ∝ (Z − 1); for Z = 25, √ν = k(25 − 1) = k·24.
Q28 — History, Laws & Modern Periodic Table · easy · numerical
For the triad S (32), Se (?), Te (127.6), the predicted atomic mass of Se is about:
A. 160
B. 48
C. 80 ✓ Correct
D. 95.8
Solution: Mean = (32 + 127.6)/2 ≈ 79.8 ≈ 79 (actual Se).
Q29 — History, Laws & Modern Periodic Table · easy · numerical
The element with atomic number 12 is in:
A. Period 2, Group 2
B. Period 4, Group 2
C. Period 3, Group 12
D. Period 3, Group 2 ✓ Correct
Solution: Mg: [Ne]3s² ⇒ period 3, group 2.
Q30 — History, Laws & Modern Periodic Table · medium · numerical
An element with valence-shell configuration ns² np⁵ belongs to group:
A. 17 ✓ Correct
B. 7
C. 5
D. 15
Solution: 2 + 5 = 7 valence electrons ⇒ group 17 (halogens).