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The Modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their:
The context clearly defines the Modern Periodic Law: 'The physical and chemical properties of the elements are periodic functions of their atomic numbers.'
Who experimentally demonstrated that atomic number is a more fundamental property of an element than its atomic mass, leading to the modification of Mendeleev's Periodic Law?
The passage states: 'In 1913, the English physicist, Henry Moseley observed regularities in the characteristic X-ray spectra of the elements... He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass.'
The Periodic Law, as it is understood today, is fundamentally a consequence of the periodic variation in:
The text says: 'In fact, it is now recognized that the Periodic Law is essentially the consequence of the periodic variation in electronic configurations, which indeed determine the physical and chemical properties of elements and their compounds.'
In 1800, approximately how many elements were known?
The context states: 'In 1800, only 31 elements were known.'
By 1865, the number of identified elements had approximately doubled to:
The text mentions: 'By 1865, the number of identified elements had more than doubled to 63.'
Moseley's work involved plotting $\sqrt{\nu}$ (where $\nu$ is the frequency of X-rays emitted) against which atomic property, yielding a straight line?
The context states: 'A plot of $\sqrt{\nu}$ (where $\nu$ is frequency of X-rays emitted) against atomic number (Z) gave a straight line and not the plot of $\sqrt{\nu}$ vs atomic mass.'
What is the primary reason scientists felt the need to classify elements?
The text explains: 'To ease out this problem, scientists searched for a systematic way to organise their knowledge by classifying the elements. Not only that it would rationalize known chemical facts about elements, but even predict new ones for undertaking further study.'
Dmitri Mendeleev's Periodic Table was primarily based on arranging elements in increasing order of their:
The summary section clearly states: 'Mendeleev’s Periodic table was based on atomic masses.'
Which of the following describes an allylic halide?
According to the NCERT text, 'Allylic halides are the compounds in which the halogen atom is bonded to an sp3-hybridised carbon atom adjacent to carbon-carbon double bond (C=C) i.e. to an allylic carbon.'
In the IUPAC system of nomenclature, how are dihalogen derivatives of benzene named?
The NCERT text states: 'For dihalogen derivatives, the prefixes o-, m-, p- are used in common system but in IUPAC system, as you have learnt in Class XI, the numerals 1,2; 1,3 and 1,4 are used.'
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