One mole of a symmetrical alkene on ozonolysis gives two moles of an aldehyde having a molecular mass of $44\text{u}$. The alkene is:

An aldehyde with molecular mass $44\text{u}$ is Acetaldehyde (${\text{CH}}_3\text{CHO}$).Mass $=(12\times 2)+(1\times 4)+16=24+4+16=44\text{u}$.Since ozonolysis of one mole of a symmetrical alkene gives two moles of ${\text{CH}}_3\text{CHO}$, the alkene must be:
$${\text{CH}}_3-\text{CH}=\text{CH}-{\text{CH}}_3\underset{{\text{Zn/H}}_2\text{O}}{\overset{{\text{O}}_3}{\to }}2{\text{CH}}_3\text{CHO}$$
The alkene is 2-butene.