101. The modern periodic law states that the physical and chemical properties of elements are periodic functions of their
ⓐ. atomic masses
ⓑ. neutron numbers only
ⓒ. atomic numbers
ⓓ. discovery dates
Correct Answer: atomic numbers
Explanation: The modern periodic law uses atomic number \(Z\) as the fundamental basis of classification. Atomic number represents the nuclear charge and fixes the number of electrons in a neutral atom. Since chemical properties depend strongly on electronic configuration, especially valence-shell configuration, properties recur when similar outer electronic patterns recur. This is why atomic number gives a more satisfactory periodic order than atomic mass. The law does not say that properties are constant; it says they repeat in a regular pattern as \(Z\) increases.
102. The phrase “periodic function of atomic number” means that when elements are arranged in increasing \(Z\),
ⓐ. their atomic masses become equal after every period
ⓑ. their properties repeat in a regular pattern after certain intervals
ⓒ. every neighbouring pair has identical chemical properties
ⓓ. neutron number becomes the only deciding factor
Correct Answer: their properties repeat in a regular pattern after certain intervals
Explanation: A periodic function shows repetition after regular intervals. In the periodic table, this repetition appears because similar valence-shell electronic configurations recur as atomic number increases. Elements with similar outer electronic arrangements often show related chemical behaviour. The repetition is not exact equality of all properties, because size, shell number, and nuclear charge also change. The modern law connects repeated properties with increasing \(Z\), not with neutron count alone.
103. If a neutral atom has \(Z=11\), it contains \(11\) electrons arranged as \(2,8,1\). The most useful conclusion for modern periodic classification is that this atom
ⓐ. must be placed only by its average atomic mass
ⓑ. has no connection between \(Z\) and chemical properties
ⓒ. must have the same properties as every element with \(11\) neutrons
ⓓ. has one valence electron and can be placed with elements having a similar outer-shell pattern
Correct Answer: has one valence electron and can be placed with elements having a similar outer-shell pattern
Explanation: Atomic number \(Z=11\) gives \(11\) electrons in a neutral atom. The electronic distribution \(2,8,1\) shows one electron in the outermost shell. Modern classification uses this link between \(Z\), electronic configuration, and properties. Elements with one valence electron often show related chemical behaviour, so they are placed in related positions of the periodic table. Neutron number can change isotopic mass, but it does not provide the main basis for ordinary chemical classification.
104. The change from Mendeleev's periodic law to the modern periodic law is best represented as
ⓐ. properties depend periodically on atomic mass \(\rightarrow\) properties depend periodically on atomic number
ⓑ. properties depend periodically on atomic number \(\rightarrow\) properties depend periodically on atomic mass
ⓒ. properties depend on alphabetical order \(\rightarrow\) properties depend on discovery date
ⓓ. properties depend on physical state only \(\rightarrow\) properties depend on colour only
Correct Answer: properties depend periodically on atomic mass \(\rightarrow\) properties depend periodically on atomic number
Explanation: Mendeleev's periodic law stated that properties of elements are periodic functions of their atomic masses. The modern periodic law replaces atomic mass with atomic number \(Z\). This change is important because \(Z\) is linked with nuclear charge and electronic configuration. It also explains isotope placement and anomalous pairs more effectively. The modern law keeps the idea of periodicity but gives it a more fundamental basis.
105. A pair of isotopes has the same \(Z\) but different mass numbers. The modern periodic law places them in the same position because
ⓐ. their atomic masses are exactly equal
ⓑ. their atomic numbers and ordinary electronic configurations are the same
ⓒ. isotopes are always placed in different groups
ⓓ. neutron number decides group number directly
Correct Answer: their atomic numbers and ordinary electronic configurations are the same
Explanation: Isotopes of the same element have the same atomic number \(Z\). In neutral atoms, the same \(Z\) gives the same number of electrons and therefore the same electronic configuration. Since the modern periodic law is based on atomic number, isotopes naturally occupy the same position. Their different mass numbers come from different neutron numbers, not different chemical identity. This is one major advantage of the modern law over an atomic-mass-based arrangement.
106. A graph is described as follows.
The x-axis shows increasing atomic number \(Z\). The y-axis shows a property that rises and falls in a repeating pattern as new periods begin and end.
The graph description is best interpreted as showing
ⓐ. periodic variation of a property with atomic number
ⓑ. random variation unrelated to classification
ⓒ. equality of atomic masses in each group
ⓓ. a fixed value of every chemical property
Correct Answer: periodic variation of a property with atomic number
Explanation: A repeating rise-and-fall pattern with increasing \(Z\) is a sign of periodicity. In the modern periodic table, properties such as atomic size, ionization enthalpy, and chemical behaviour show systematic trends with atomic number. The repeating pattern arises because valence-shell configurations recur after intervals. The graph does not mean that the property stays constant for all elements. It shows regular recurrence linked with atomic number, which is the core idea of the modern periodic law.
107. Consider the statements below.
I. Modern periodic law uses atomic number as the basis.
II. The repetition of properties is connected with recurrence of similar valence-shell configurations.
III. Isotopes require separate positions in the modern periodic table because their masses differ.
IV. Atomic number is linked with nuclear charge.
The supported statements are
ⓐ. I and III only
ⓑ. II and III only
ⓒ. I, II, and IV only
ⓓ. I, II, III, and IV
Correct Answer: I, II, and IV only
Explanation: Statement I is supported because the modern periodic law is based on atomic number \(Z\). Statement II is also supported because similar valence-shell configurations recur as \(Z\) increases, producing periodicity in properties. Statement IV is true because atomic number represents nuclear charge in units of proton charge. Statement III is not valid because isotopes of the same element have the same \(Z\) and occupy the same position. The modern law solves the isotope difficulty by using \(Z\), not mass number, as the deciding basis.
108. The table gives two neutral atoms with their electronic distributions.
| Atom | Atomic number | Electronic distribution |
|---|
| P | \(3\) | \(2,1\) |
| Q | \(11\) | \(2,8,1\) |
The reason these atoms show related group behaviour is that both
ⓐ. have the same total number of electrons
ⓑ. have the same atomic mass
ⓒ. contain the same number of occupied shells
ⓓ. have one electron in the outermost shell
Correct Answer: have one electron in the outermost shell
Explanation: Atom P with distribution \(2,1\) has one valence electron. Atom Q with distribution \(2,8,1\) also has one valence electron. The total number of electrons and the number of occupied shells are different, but the valence-shell pattern is similar. Modern periodic classification uses this recurrence of outer electronic configuration to explain group similarity. Similar valence electron count often leads to similar chemical behaviour, even though size and shell number change down the group.
109. Assertion: Atomic number is a better basis than atomic mass for the modern periodic table.
Reason: Atomic number determines the electronic configuration of a neutral atom, and electronic configuration strongly influences chemical properties.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Assertion is true, but Reason is false
ⓒ. Both Assertion and Reason are true, and Reason explains Assertion
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: The Assertion is true because the modern periodic table is arranged according to atomic number. The Reason is also true because a neutral atom has electrons equal to \(Z\), and these electrons occupy shells and subshells in a definite pattern. The outer electronic configuration controls many chemical properties, including valency and type of compounds formed. Therefore, atomic number gives a direct route to chemical periodicity. Atomic mass does not provide this connection as clearly, especially in the case of isotopes and anomalous mass-order pairs.
110. A neutral element \(X\) has \(Z=9\), and another neutral element \(Y\) has \(Z=17\). Their electronic distributions are \(2,7\) and \(2,8,7\), respectively. The modern periodic-table reason for their similarity is
ⓐ. both have the same number of shells
ⓑ. both have \(7\) valence electrons
ⓒ. both have equal atomic masses
ⓓ. both have \(17\) protons
Correct Answer: both have \(7\) valence electrons
Explanation: \( \textbf{Given for \(X\):} \) \(Z=9\), so a neutral atom has \(9\) electrons.
\( \textbf{Distribution of \(X\):} \) \(2,7\), so valence electrons \(=7\).
\( \textbf{Given for \(Y\):} \) \(Z=17\), so a neutral atom has \(17\) electrons.
\( \textbf{Distribution of \(Y\):} \) \(2,8,7\), so valence electrons \(=7\).
\( \textbf{Modern classification idea:} \) Similar valence-shell configuration leads to related chemical behaviour.
\( \textbf{Shell comparison:} \) \(X\) has \(2\) occupied shells, while \(Y\) has \(3\), so shell number is not the shared feature.
\( \textbf{Proton comparison:} \) \(X\) has \(9\) protons and \(Y\) has \(17\), so proton number is not equal.
\( \textbf{Final answer:} \) The shared \(7\)-valence-electron pattern explains their group similarity. The key comparison is the outer shell, not the total electron count.
111. A classification note says: “When \(Z\) increases, electrons are added according to definite shell and subshell patterns. After certain intervals, similar outer configurations appear again.” This note explains
ⓐ. why periodicity is related to electronic configuration
ⓑ. why elements must be arranged alphabetically
ⓒ. why all atomic masses are whole numbers
ⓓ. why isotopes must occupy different groups
Correct Answer: why periodicity is related to electronic configuration
Explanation: The note connects increasing atomic number with electron filling. As electrons enter shells and subshells in an orderly way, similar outer configurations recur. These recurring valence-shell patterns produce recurring chemical properties. This is the electronic-configuration explanation of modern periodicity. Alphabetical order, whole-number atomic masses, and separate isotope groups do not explain the repeating chemical pattern.
112. The most suitable correction to the statement “Modern periodic law is only Mendeleev's law with different words” is that modern periodic law
ⓐ. changes the fundamental basis from atomic mass to atomic number and links periodicity with electronic configuration
ⓑ. removes all chemical properties from classification
ⓒ. uses atomic mass more strictly than Mendeleev did
ⓓ. arranges elements by the first letter of their symbols
Correct Answer: changes the fundamental basis from atomic mass to atomic number and links periodicity with electronic configuration
Explanation: The modern periodic law retains the idea that properties repeat periodically. However, it changes the basis from atomic mass to atomic number \(Z\). This is not a minor wording change because \(Z\) is tied to nuclear charge and the electronic configuration of neutral atoms. The law explains why similar valence-shell arrangements recur and why elements in the same group behave similarly. It also handles isotopes and anomalous pairs more naturally than the older mass-based law.
113. In the modern periodic table, the chemical properties of elements are mainly connected with the configuration of the
ⓐ. nucleus only
ⓑ. neutron cloud
ⓒ. average atomic mass value only
ⓓ. valence shell
Correct Answer: valence shell
Explanation: Chemical properties depend strongly on the electrons involved in bonding and reactions. These are mainly the electrons in the outermost occupied shell, called the valence shell. Modern periodicity is explained by the recurrence of similar valence-shell configurations. The nucleus determines \(Z\), and \(Z\) determines the electron arrangement in a neutral atom, but ordinary chemical behaviour is expressed through the outer electrons. Average atomic mass alone cannot explain why elements in a group have similar valency and compound formation.
114. The row in the table that best represents a valid modern-periodic-law link is
| Row | Basis | Reason for recurring properties |
|---|
| P | Atomic mass | Exact repetition of neutron number |
| Q | Atomic number \(Z\) | Recurrence of similar valence-shell configurations |
| R | Element name | Same first letter gives similar reactivity |
| S | Physical state | All gases show identical valency |
ⓐ. Row P
ⓑ. Row R
ⓒ. Row S
ⓓ. Row Q
Correct Answer: Row Q
Explanation: Row Q correctly connects atomic number \(Z\) with recurring valence-shell configurations. This is the modern explanation for periodicity in chemical properties. Row P incorrectly uses atomic mass and neutron repetition as the reason. Row R is not scientific because element names do not determine reactivity. Row S is also weak because physical state alone does not decide valency or periodic position. The modern table is based on \(Z\) and the electronic pattern that follows from it.
115. Compare two neutral atoms: one has \(Z=12\) and electronic distribution \(2,8,2\), while the other has \(Z=20\) and distribution \(2,8,8,2\). Their related behaviour in modern classification is best linked to
ⓐ. the same number of total electrons
ⓑ. the same number of valence electrons
ⓒ. identical atomic masses
ⓓ. absence of inner shells
Correct Answer: the same number of valence electrons
Explanation: \( \textbf{First atom:} \) \(Z=12\), so the neutral atom has \(12\) electrons.
\( \textbf{Distribution:} \) \(2,8,2\), so the outermost shell contains \(2\) electrons.
\( \textbf{Second atom:} \) \(Z=20\), so the neutral atom has \(20\) electrons.
\( \textbf{Distribution:} \) \(2,8,8,2\), so the outermost shell again contains \(2\) electrons.
\( \textbf{Classification link:} \) Same valence-electron count often gives similar group behaviour in representative elements.
\( \textbf{Not the total count:} \) \(12\) electrons and \(20\) electrons are not equal.
\( \textbf{Not the mass basis:} \) Similarity is not being inferred from identical atomic masses.
\( \textbf{Final answer:} \) The shared outer-shell pattern of \(2\) valence electrons is the classification clue. The extra inner shell changes size but not the basic group similarity.
116. The statement “properties are periodic functions of \(Z\)” should not be misread to mean that
ⓐ. every property of the eighth or eighteenth element is exactly identical to the first
ⓑ. properties repeat in a regular way as \(Z\) increases
ⓒ. similar valence-shell configurations recur
ⓓ. electronic configuration helps explain periodicity
Correct Answer: every property of the eighth or eighteenth element is exactly identical to the first
Explanation: Periodicity means regular recurrence of similar properties, not exact duplication of every property. Elements in a group may have similar valence-shell configurations and related chemical behaviour. However, atomic size, mass, density, reactivity strength, and other properties can change down a group. The modern law explains patterns and trends rather than claiming perfect identity. This distinction is important because similarity and sameness are not the same idea in periodic classification.
117. The long-form modern periodic table contains
ⓐ. \(8\) periods and \(7\) groups
ⓑ. \(18\) periods and \(7\) groups
ⓒ. \(7\) periods and \(18\) groups
ⓓ. \(3\) periods and \(8\) groups
Correct Answer: \(7\) periods and \(18\) groups
Explanation: The long-form modern periodic table is arranged into \(7\) horizontal periods and \(18\) vertical groups. Periods show the filling of principal shells as atomic number increases. Groups collect elements with related outer electronic configurations and similar properties. This layout is more systematic than earlier shorter arrangements. Remembering the row-column structure helps later in identifying period, group, and block from electronic configuration.
118. In the long-form periodic table, atomic number generally increases
ⓐ. from right to left only and then upward
ⓑ. from left to right across a period and from top to bottom down the table
ⓒ. randomly without any fixed direction
ⓓ. only within noble gases
Correct Answer: from left to right across a period and from top to bottom down the table
Explanation: Elements in the modern periodic table are arranged in increasing atomic number. Across a period, \(Z\) increases step by step from left to right. After a period ends, the next period begins below, so \(Z\) also increases as one moves through the table from top to bottom in sequence. This order is tied to progressive electron filling. The arrangement is not random because atomic number is the organizing principle of the modern table.
119. The separate placement of lanthanoids and actinoids below the main body of the periodic table is mainly done to
ⓐ. show that these elements have no atomic numbers
ⓑ. place all non-metals outside the periodic table
ⓒ. prove that they are isotopes of each other
ⓓ. keep the main table compact while showing the inner-transition series
Correct Answer: keep the main table compact while showing the inner-transition series
Explanation: Lanthanoids and actinoids belong to the inner-transition series. They are usually shown below the main body of the periodic table to keep the table from becoming too wide. This separate display does not mean they are outside periodic classification. They still have definite atomic numbers and positions in the extended sequence. The arrangement is a practical layout choice that preserves both compactness and electronic-configuration logic.
120. A simplified periodic-table layout is described as follows: seven horizontal rows are present, eighteen vertical columns are used, and two series are shown separately below the main body. This layout corresponds to
ⓐ. Dobereiner's triads
ⓑ. Newlands' octave arrangement
ⓒ. the long-form modern periodic table
ⓓ. a list arranged only by atomic mass
Correct Answer: the long-form modern periodic table
Explanation: The description matches the long-form modern periodic table. It has \(7\) periods, \(18\) groups, and separate rows for the lanthanoids and actinoids. Dobereiner's triads involved groups of three elements, not a full table. Newlands' arrangement used the octave idea and did not have the modern \(18\)-group layout. The long-form table reflects atomic-number order and electronic-configuration structure.
