<span>Slab pull” is a type of tectonic plate movement
that occurs due to the forces of mantle convection and results in the
subduction of the lithosphere, causing earthquakes. Slab pulls are actually
portions of the motions of a tectonic plate that accounts for its subduction.
The motion of these plates are driven by weight of cold and denser plates that
sink at trenches towards the mantle of the Earth. </span>
<u>Answer:</u> The correct answer is Option b.
<u>Explanation:</u>
Nuclear fusion reaction is defined as the reaction in which lighter nuclei combine together to form a single heavier nuclei.
Another name for helium nuclei is alpha particle.
For the given options:
- <u>Option a:</u> The CNO cycle
This cycle is named as carbon-nitrogen-oxygen cycle. In this cycle, carbon absorbs a proton to form nitrogen which further absorbs a photon to form oxygen. Thus, helium particles are not getting fused in this process.
- <u>Option b:</u> The triple alpha process
This process is a set of nuclear reaction in which 3 alpha or helium nuclei combine together to form carbon nucleus.
The equation representing the fusion process follows:

- <u>Option c:</u> Photo dissociation
This is defined as the process in which a chemical compound is broken down by photons. Thus, helium particles are not getting fused in this process.
- <u>Option d:</u> The proton-proton chain
This process is a set of nuclear fusion reactions by which stars convert hydrogen nucleus to helium nucleus. The chemical reactions for this process are:

Here, fusion of protons takes place.
Hence, the correct answer is Option b.
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