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The incorrect IUPAC name is : -
A
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B
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C
$CH_3-C\equiv C-CH(CH_3)_2$ : 4-methyl-2-pentyne
D
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Detailed Solution
$CH_3COCH(CH_3)CH_3$: the principal functional group (C=O) must get the lowest possible number. Numbering from the left end gives C=O at C-2 and the methyl at C-3. So the correct name is 3-methyl-2-butanone (3-methylbutan-2-one), and '2-methyl-3-butanone' is incorrect.
$CH_3CH(CH_3)CH(C_2H_5)CH_3$: the longest chain has five carbons (through the ethyl group), with methyls at C-2 and C-3: 2,3-dimethylpentane; correct.
$CH_3C\equiv CCH(CH_3)_2$: five-carbon chain, triple bond at C-2, methyl at C-4: 4-methyl-2-pentyne; correct.
$CH_3CHClCHBrCH_3$: halogens at 2 and 3 either way; alphabetical order gives bromo the lower number: 2-bromo-3-chlorobutane; correct.
So the incorrect IUPAC name is 2-methyl-3-butanone.
$CH_3CH(CH_3)CH(C_2H_5)CH_3$: the longest chain has five carbons (through the ethyl group), with methyls at C-2 and C-3: 2,3-dimethylpentane; correct.
$CH_3C\equiv CCH(CH_3)_2$: five-carbon chain, triple bond at C-2, methyl at C-4: 4-methyl-2-pentyne; correct.
$CH_3CHClCHBrCH_3$: halogens at 2 and 3 either way; alphabetical order gives bromo the lower number: 2-bromo-3-chlorobutane; correct.
So the incorrect IUPAC name is 2-methyl-3-butanone.