is most reactive for electrophilic addition reaction, due to electron donating effect of oxygen adjacent to double bond that readily favours the attack to E⊕.
Among other options such as alkenes and alkynes, alkenes gives fast electrophilic addition reaction. This is because when a proton adds to an alkene, an alkyl cation is formed and when a proton adds to an alkyne, a vinylic cation is formed. A vinylic cation is less stable than alkyl cation. Hence alkenes are more reactive for electrophilic addition. In
1
C
H3−
2
C
H=
3
C
H−
O
∥
C
4
−O
5
C
H3 due to resonance C2−C3 has less electron density, hence it won't undergo electrophilic addition easily. CH3−CN=CN−