Ans. In trans-but-2-ene, the dipole moment of two C-CH3 bonds are equal and opposite and hence they exactly cancel out each other. Thus trans-but-2-ene is non polar. In trans-pent-2-ene, the dipole moments of C-CH3 and C-CH2CH3 bonds are unequal. Although these two dipoles oppose each other, yet they do not exactly cancel out each other and hence trans-pent2-ene has a small value of dipole moment and thus is polar.