Practice free Chemistry NEET multiple-choice questions online with instant answers and detailed explanations. No login required.
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.'
What is the classification of $CH_3CH=CHC(Br)(CH_3)_2$?
In $CH_3CH=CHC(Br)(CH_3)_2$, the double bond is between two carbons, and the bromine is attached to a carbon atom that is one carbon away from the double bond ($sp^3$ hybridised carbon next to an $sp^2$ carbon of the double bond). This fits the definition of an allylic halide: 'These are the compounds in which the halogen atom is bonded to an sp3-hybridised carbon atom adjacent to carbon-carbon double bond (C=C).'
What is the IUPAC name for neo-Pentyl bromide?
According to Table 6.1 in the NCERT text, the common name 'neo-Pentyl bromide' corresponds to the IUPAC name '1-Bromo-2,2-dimethylpropane'.
Which of the following compounds is an example of a gem-dihalide?
The NCERT text defines geminal halides or gem-dihalides as compounds 'when both the halogen atoms are present on the same carbon atom of the chain'. 1,1-Dibromoethane has both bromine atoms on the same carbon.
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