Nuclear fusion

The CED states fusion at 15.7.A.6: two or more smaller nuclei combine to form a larger nucleus, as well as subatomic particles. The energy accounting is identical to fission's: if the product is more tightly bound per nucleon, the total mass falls and the difference leaves as energy through $E = mc^2$ (15.7.A.4), as kinetic energy of the products or as photons (15.7.A.5).

Getting two nuclei close enough is the difficulty. Both carry positive charge, so Coulomb's law gives a repulsion growing as $1/r^2$ all the way in, while the strong force that would bind them acts only at nuclear range (15.7.A.1). The nuclei therefore need enough kinetic energy on approach to cross that electrostatic barrier, which is why fusion demands extreme temperature and density. The barrier is commonly named the Coulomb barrier.

Be careful how much of that you attribute to the course. The required content on fusion is 15.7.A.6 plus the conservation constraints in 15.7.A.2 and 15.7.A.3. The CED says nothing about the conditions fusion needs, does not use the phrase Coulomb barrier, and, unlike fission at 15.7.A.8, makes no statement about whether fusion happens spontaneously. The paragraph above is built from Coulomb's law and 15.7.A.1, not quoted from the framework.

Nucleon number is conserved here as in any nuclear reaction, so a fusion equation balances the same way a fission one does.