The correct option is D But-2-ene
Molecular formula of an aldehyde is CnH2nO
n×12+2n×1+16=44⇒n=2
So, the molecular formula will be C2H4O
The aldehyde with molecular mass 44u is CH3CHO (acetaldehyde).
Therefore, the symmetrical alkene is but-2-ene.
CH3CH=CHCH3(i) O3−−−−−−−→(ii) Zn/H2O2CH3CHO
Hence, option (d) is correct.