Which of the following compounds shall not produce propene by reaction with HBr followed by elimination or direct only elimination reaction ?

Which one of the following structures represent nylon 6,6 polymer ?

In which of the following molecules, all atoms are coplanar ?

Which of the following can be used as the halide component for Freidel –Crafts reaction?

Jahn-Teller effect is not observed in high spin complexes of