Among the following, the elements with even number of neutrons is

The formula for neutrons is n= A- Z

For ${}_{11}{}^{23}\mathrm{Na}\to \mathrm{n}=23-11=12$

For${}_{13}{}^{27}\mathrm{Al}\to \mathrm{n}=27-13=14\left(\mathrm{Even}\right)$

For${}_{10}{}^{20}\mathrm{Ne}\to \mathrm{n}=20-10=10\left(\mathrm{even}\right)$

For ${}_2{}^4\mathrm{He}\to \mathrm{n}=4-2=2\left(\mathrm{Even}\right)$

Hence, all the options are correct.