JEE Chemistry 2025 Question with Solution

Given: Statements about geometrical isomerism are to be checked for correctness.

Find: Which statements are incorrect, and hence the correct option.

The key condition for geometrical isomerism is that each carbon atom of the double bond must have two different groups attached to it.

1. Statement (A): Propene shows geometrical isomerism.

Propene is $\mathrm{CH_3-CH=CH_2}$. One of the double-bonded carbon atoms has two identical hydrogen atoms, so geometrical isomerism is not possible. Therefore, (A) is incorrect.

2. Statement (B): Trans isomer has identical atoms/groups on the opposite sides of the double bond.

This is the definition of a trans isomer. Therefore, (B) is correct.

3. Statement (C): Cis-but-2-ene has higher dipole moment than trans-but-2-ene.

In the cis isomer, bond dipoles do not cancel effectively, so its dipole moment is higher than that of the trans isomer. Therefore, (C) is correct.

4. Statement (D): 2-methylbut-2-ene shows two geometrical isomers.

2-methylbut-2-ene is $\mathrm{(CH_3)_2C=CH-CH_3}$. One carbon of the double bond has two identical methyl groups, so geometrical isomerism is not possible. Therefore, (D) is incorrect.

5. Statement (E): Trans-isomer has lower melting point than cis isomer.

Trans isomers are generally more symmetrical and pack better in the crystal lattice, so they usually have higher melting points than cis isomers. Hence this statement is opposite to the usual trend, so (E) is incorrect.

Thus, the incorrect statements are (A), (D) and (E) only.

Therefore, the correct option is A.