Hydrogen bomb is based on
A. Controlled chain reaction
B. Uncontrolled chain reaction
C. Nuclear fusion
D. Nuclear fission

Hint: As the name suggests, fusion of hydrogen takes place in a hydrogen bomb. As hydrogen just has an electron and a proton, it cannot take part in nuclear fission. Nuclear fusion is the only feasible option to release such a high magnitude of energy.

Complete step by step answer:
A hydrogen bomb is a nuclear fusion based bomb. Here two light nuclei fuse to for a bigger nucleus and in the process releases a large amount of energy. In a hydrogen bomb, two isotopes of hydrogen i.e., deuterium and tritium fuses to give a helium and a neutron. This fusion releases 17.6 MeV of energy.
So the answer is option C.

Additional information:
Hydrogen bombs cause a bigger explosion than an atomic bomb. The shock waves, blast, heat and radiation are more widespread making it 1000 times more dangerous in comparison to an atomic bomb. The range of destruction of a hydrogen bomb is 5 to 10 miles. As it is aided by nuclear fusion, it becomes uncontrolled.
In a nuclear fusion, the difference in masses between the products and the reactants is considered to contribute to the energy release. This difference in mass is known as mass defect.

Note:
A few decades ago it was considered that nuclear fusion is only possible in the stars. This is because it is difficult to channel or control such high energy release during the process. At sufficiently high temperature, matter can undergo fusion due to collisions with extreme thermal kinetic energies. Inertial confinement fusion (ICF) is a method focused at releasing high magnitudes of energy by heating and compressing a fuel target. The fuel used is a pellet of tritium and deuterium.