Which is incorrect IUPAC name:-(A)- 3-Pentyne(B)- 3-Methyl-2-butanone(C)- 2-Ethyl-3-methyl-1-butene(D)- 3-Ethyl-2-methyl pentane

The incorrect IUPAC name among the given options is (D) 3-Ethyl-2-methylpentane. Here's why:

(A) 3-Pentyne: This name is correct. It refers to a molecule with a triple bond starting at the third carbon of a five-carbon chain (pentyne).

(B) 3-Methyl-2-butanone: This name is correct. It refers to a four-carbon ketone (butanone) with a methyl group attached to the third carbon.

(C) 2-Ethyl-3-methyl-1-butene: This name is correct. It refers to a four-carbon chain (butene) with a double bond starting at the first carbon, an ethyl group on the second carbon, and a methyl group on the third carbon.

(D) 3-Ethyl-2-methylpentane: This name is incorrect. According to IUPAC rules, the longest carbon chain should be identified first, and substituents should be named and numbered to give the lowest possible numbers to the substituents. The correct name for this compound should be 3-Methyl-4-ethylhexane, because the longest chain here is actually six carbons (hexane) and not five (pentane).

Therefore, the incorrect IUPAC name is (D) 3-Ethyl-2-methylpentane.