Distinguish between nuclear fission and fusion. Show how in both these processes energy is released. Calculate the energy release in MeV in the deuterium-tritium fusion reaction : 
${}_1^{2}H{+}_1^{3}H{\to }_1^{4}He{+}_0{n}^1$
Using the data:
$m{(}_1^{2}H)=2.014102u$
$m{(}_1^{3}H)=3.016049u$
$m{(}_2^{4}He)=4.002603u$
$mn=1.008665u$
$lu=931.5MeV/c2$

Nuclear fission is a process of splitting of a heavier nucleus into two lighter nuclei. It generally occurs in elements of high atomic mass.

Nuclear fusion is a process of combination of two light nuclei to form a heavier nuclei. It generally occurs in elements of low atomic mass.

In both the processes, the total mass of the products is slightly less than the mass of the original nuclei. This difference in mass is converted to energy.

In the given problem, mass defect is

$\Delta m=2.014102+3.016049-4.002603-1.008665$

$\Delta m=0.018883u$

Energy released, $\Delta E=\Delta m{c}^2$

$\Delta E=0.018883\times 931.5=17.589MeV$