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Classification of Elements and Periodicity in Properties — NEET & JEE MCQs with answers
Unit 3 covers the historical development and modern form of the Periodic Table, the classification of elements into s, p, d, and f blocks, and periodic trends in atomic radius, ionization enthalpy, electron gain enthalpy, electronegativity, valence, and chemical reactivity. Understanding periodicity allows prediction of element behaviour from position in the table.
Topics in this chapter
- 3.1 Why Do We Need to Classify Elements?
- 3.2 Genesis of Periodic Classification
- 3.3 Modern Periodic Law and the Present Form of the Periodic Table
- 3.4 Nomenclature of Elements with Atomic Numbers > 100
- 3.5 Electronic Configurations of Elements and the Periodic Table
- 3.6 Electronic Configurations and Types of Elements: s-, p-, d-, f-Blocks
- 3.7 Periodic Trends in Properties of Elements
Free practice questions
Moseley's X-ray work established that the more fundamental property of an element is its:
- A. atomic mass
- B. equivalent weight
- C. atomic number
- D. atomic volume
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Answer: C — He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass.
NCERT Class 11 Chemistry Ch 3
For which of the three triads in NCERT Table 3.1 is the atomic weight of the middle element EXACTLY equal to the mean of the other two?
- A. None of the three triads
- B. Ca, Sr, Ba
- C. Cl, Br, I
- D. Li, Na, K
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Answer: D — For Li/Na/K, $\dfrac{7+39}{2}=23$, exactly the atomic weight of Na. For Ca/Sr/Ba the mean is 88.5 against Sr = 88, and for Cl/Br/I it is 81.25 against Br = 80 — both only approximate.
NCERT Class 11 Chemistry Ch 3
In IUPAC numerical roots, the digit 3 is represented by:
- A. tri
- B. tre
- C. ter
- D. trio
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Answer: A — NCERT Table 3.4: digit 3 = tri (abbreviation t).
NCERT Class 11 Chemistry · Ch 3 · 3.6 Electronic Structure of Atoms and the Periodic Table
According to Table 3.5 of NCERT, the officially accepted IUPAC name of the element with atomic number 101 is:
- A. Rutherfordium
- B. Nobelium
- C. Lawrencium
- D. Mendelevium
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Answer: D — Table 3.5 lists element 101 as Mendelevium (systematic name Unnilunium).
NCERT Class 11 Chemistry Ch 3
On the Pauling scale, the element arbitrarily assigned a value of 4.0 (the highest) is:
- A. Chlorine
- B. Oxygen
- C. Fluorine
- D. Nitrogen
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Answer: C — NCERT: Linus Pauling assigned a value of 4.0 to fluorine, the element considered to have the greatest ability to attract electrons.
NCERT Class 11 Chemistry · Ch 3 · 3.7 Periodic Trends in Properties of Elements
The fifth period begins with which element?
- A. Caesium
- B. Rubidium
- C. Yttrium
- D. Potassium
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Answer: B — NCERT states that the fifth period ($n = 5$) begins with rubidium and is similar to the fourth period, containing the $4d$ transition series.
NCERT Class 11 Chemistry Ch 3.5
According to NCERT, how many elements were known in the year 1800?
- A. 92
- B. 114
- C. 63
- D. 31
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Answer: D — NCERT states: 'In 1800, only 31 elements were known.' The figure 63 is the count by 1865 and 114 is the number known at present.
NCERT Class 11 Chemistry Ch 3
The German chemist who, in the early 1800s, was the first to consider the idea of trends among the properties of elements and noted similarities among groups of three elements was:
- A. Henry Moseley
- B. Dmitri Mendeleev
- C. Johann Dobereiner
- D. John Newlands
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Answer: C — NCERT credits Johann Dobereiner as the first to consider trends among properties of elements; by 1829 he noted similarities among groups of three elements (Triads).
NCERT Class 11 Chemistry · Ch 3 · 3.6 Electronic Structure of Atoms and the Periodic Table
The sum of the atomic weights of the three elements of the triad Li, Na, K as given in NCERT is:
- A. 62
- B. 69
- C. 46
- D. 70
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Answer: B — $7+23+39=69$. Note that one-third of this sum, $69/3=23$, is exactly the atomic weight of the middle element Na.
NCERT Class 11 Chemistry Ch 3
Beryllium has four electrons; NCERT gives its electronic configuration as:
- A. $1s^2 2p^2$
- B. $1s^2 2s^2$
- C. $1s^2 2s^2 2p^2$
- D. $1s^2 2s^1 2p^1$
Show answer
Answer: B — NCERT states that after lithium the next element, beryllium, has four electrons and has the electronic configuration $1s^2 2s^2$.
NCERT Class 11 Chemistry Ch 3.5
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