Rank the hydrogen atoms $(H_a, H_b, H_c)$ present in the following molecule in decreasing order of their acidic strength.

Which of the following can show $+M$ or $+R$ effect?

Which of the following orders of rotation barrier about the $C=C$ bond,as indicated in the structures $(I)$,$(II)$,and $(III)$,is correct?

Which of the following statements are not correct?
$a$. The energy of resonance hybrid structure is higher than that of the possible canonical structures of the molecule.
$b$. When inductive effect and electromeric effect operate in opposite directions,electromeric effect predominates.
$c$. When the $\pi$ electrons of the multiple bond are transferred to that atom to which the attacking reagent does not get attached,it is known as $+E$ effect.
$d$. The resonance structures with separation of opposite charges are more stable.

Identify the group that exerts electron withdrawing resonance effect.

Which of the following groups exhibits $(+)R$ effect?